とりあえず何が定義されてるか調べてみた。
__PPU__, __SPU__ で判断すればいいみたい。
追記:__PPU__ があると思ったのは勘違い。
Fedora 5 の gcc
$ gcc -x c -arch=ppc64 -maltivec -mpowerpc64 -dM -E /dev/null
#define __DBL_MIN_EXP__ (-1021)
#define __FLT_MIN__ 1.17549435e-38F
#define __VEC__ 10206
#define __CHAR_BIT__ 8
#define __WCHAR_MAX__ 2147483647
#define __DBL_DENORM_MIN__ 4.9406564584124654e-324
#define __ALTIVEC__ 1
#define __FLT_EVAL_METHOD__ 0
#define __FINITE_MATH_ONLY__ 0
#define __GNUC_PATCHLEVEL__ 0
#define __SHRT_MAX__ 32767
#define __LDBL_MAX__ 1.79769313486231580793728971405301e+308L
#define __linux 1
#define __CHAR_UNSIGNED__ 1
#define __LDBL_MAX_EXP__ 1024
#define __linux__ 1
#define __SCHAR_MAX__ 127
#define __USER_LABEL_PREFIX__
#define __LDBL_HAS_INFINITY__ 1
#define __DBL_DIG__ 15
#define __FLT_EPSILON__ 1.19209290e-7F
#define _CALL_SYSV 1
#define __LDBL_MIN__ 2.00416836000897277799610805135016e-292L
#define __unix__ 1
#define __DECIMAL_DIG__ 33
#define __gnu_linux__ 1
#define __LDBL_HAS_QUIET_NAN__ 1
#define __GNUC__ 4
#define __DBL_MAX__ 1.7976931348623157e+308
#define __DBL_HAS_INFINITY__ 1
#define __DBL_MAX_EXP__ 1024
#define __LONG_LONG_MAX__ 9223372036854775807LL
#define __PPC__ 1
#define __GXX_ABI_VERSION 1002
#define __FLT_MIN_EXP__ (-125)
#define __DBL_MIN__ 2.2250738585072014e-308
#define __DBL_HAS_QUIET_NAN__ 1
#define __pixel __attribute__((altivec(pixel__))) unsigned short
#define __REGISTER_PREFIX__
#define __NO_INLINE__ 1
#define _ARCH_PPC 1
#define __FLT_MANT_DIG__ 24
#define __VERSION__ "4.1.0 20060304 (Red Hat 4.1.0-3)"
#define __BIG_ENDIAN__ 1
#define __UINTMAX_TYPE__ long long unsigned int
#define __powerpc__ 1
#define unix 1
#define __SIZE_TYPE__ unsigned int
#define __ELF__ 1
#define __FLT_RADIX__ 2
#define __LDBL_EPSILON__ 4.94065645841246544176568792868221e-324L
#define __GNUC_RH_RELEASE__ 3
#define __DBL_MIN_10_EXP__ (-307)
#define __LDBL_DIG__ 31
#define __vector __attribute__((altivec(vector__)))
#define __FLT_HAS_QUIET_NAN__ 1
#define __bool __attribute__((altivec(bool__))) unsigned
#define __FLT_MAX_10_EXP__ 38
#define __LONG_MAX__ 2147483647L
#define __FLT_HAS_INFINITY__ 1
#define __unix 1
#define _BIG_ENDIAN 1
#define linux 1
#define __PPC 1
#define __LDBL_MANT_DIG__ 106
#define __WCHAR_TYPE__ long int
#define __FLT_DIG__ 6
#define __powerpc 1
#define __INT_MAX__ 2147483647
#define __LONG_DOUBLE_128__ 1
#define __FLT_MAX_EXP__ 128
#define __DBL_MANT_DIG__ 53
#define __WINT_TYPE__ unsigned int
#define __STDC_HOSTED__ 1
#define __LDBL_MIN_EXP__ (-968)
#define __LDBL_MAX_10_EXP__ 308
#define __DBL_EPSILON__ 2.2204460492503131e-16
#define PPC 1
#define powerpc 1
#define __INTMAX_MAX__ 9223372036854775807LL
#define __FLT_DENORM_MIN__ 1.40129846e-45F
#define __FLT_MAX__ 3.40282347e+38F
#define __FLT_MIN_10_EXP__ (-37)
#define __INTMAX_TYPE__ long long int
#define __GNUC_MINOR__ 1
#define __DBL_MAX_10_EXP__ 308
#define __LDBL_DENORM_MIN__ 4.94065645841246544176568792868221e-324L
#define __STDC__ 1
#define __PTRDIFF_TYPE__ int
#define _ARCH_PPC64 1
#define __LDBL_MIN_10_EXP__ (-291)
PPU
$ ppu-gcc -x c -dM -E /dev/null
#define __DBL_MIN_EXP__ (-1021)
#define __FLT_MIN__ 1.17549435e-38F
#define __VEC__ 10206
#define __CHAR_BIT__ 8
#define __PPC64__ 1
#define __WCHAR_MAX__ 2147483647
#define __DBL_DENORM_MIN__ 4.9406564584124654e-324
#define __ALTIVEC__ 1
#define __FLT_EVAL_METHOD__ 0
#define pixel pixel
#define bool bool
#define __DBL_MIN_10_EXP__ (-307)
#define __FINITE_MATH_ONLY__ 0
#define __GNUC_PATCHLEVEL__ 2
#define __SHRT_MAX__ 32767
#define __LDBL_MAX__ 1.7976931348623157e+308L
#define __UINTMAX_TYPE__ long unsigned int
#define __linux 1
#define __CHAR_UNSIGNED__ 1
#define __LDBL_MAX_EXP__ 1024
#define __linux__ 1
#define __SCHAR_MAX__ 127
#define vector vector
#define __USER_LABEL_PREFIX__
#define __STDC_HOSTED__ 1
#define __LDBL_HAS_INFINITY__ 1
#define __DBL_DIG__ 15
#define __FLT_EPSILON__ 1.19209290e-7F
#define __LDBL_MIN__ 2.2250738585072014e-308L
#define __unix__ 1
#define __DECIMAL_DIG__ 17
#define __gnu_linux__ 1
#define __LDBL_HAS_QUIET_NAN__ 1
#define __GNUC__ 4
#define __DBL_MAX__ 1.7976931348623157e+308
#define __DBL_HAS_INFINITY__ 1
#define __DBL_MAX_EXP__ 1024
#define __LONG_LONG_MAX__ 9223372036854775807LL
#define __PPC__ 1
#define __GXX_ABI_VERSION 1002
#define __FLT_MIN_EXP__ (-125)
#define __DBL_MIN__ 2.2250738585072014e-308
#define __LP64__ 1
#define __DBL_HAS_QUIET_NAN__ 1
#define __pixel __attribute__((altivec(pixel__))) unsigned short
#define __REGISTER_PREFIX__
#define __NO_INLINE__ 1
#define _ARCH_PPC 1
#define __FLT_MANT_DIG__ 24
#define __VERSION__ "4.0.2 (CELL 3-2, Apr 11 2006)"
#define __BIG_ENDIAN__ 1
#define __powerpc64__ 1
#define __powerpc__ 1
#define unix 1
#define __SIZE_TYPE__ long unsigned int
#define __ELF__ 1
#define __FLT_RADIX__ 2
#define __LDBL_EPSILON__ 2.2204460492503131e-16L
#define __vector __attribute__((altivec(vector__)))
#define __FLT_HAS_QUIET_NAN__ 1
#define __bool __attribute__((altivec(bool__))) unsigned
#define __FLT_MAX_10_EXP__ 38
#define __LONG_MAX__ 9223372036854775807L
#define __FLT_HAS_INFINITY__ 1
#define __unix 1
#define _BIG_ENDIAN 1
#define linux 1
#define __LDBL_MANT_DIG__ 53
#define __WCHAR_TYPE__ int
#define __FLT_DIG__ 6
#define __INT_MAX__ 2147483647
#define __FLT_MAX_EXP__ 128
#define __DBL_MANT_DIG__ 53
#define __WINT_TYPE__ unsigned int
#define __LDBL_MIN_EXP__ (-1021)
#define __LDBL_MAX_10_EXP__ 308
#define __DBL_EPSILON__ 2.2204460492503131e-16
#define _LP64 1
#define __APPLE_ALTIVEC__ 1
#define __INTMAX_MAX__ 9223372036854775807L
#define __FLT_DENORM_MIN__ 1.40129846e-45F
#define _CALL_AIX 1
#define __PIC__ 1
#define __FLT_MAX__ 3.40282347e+38F
#define __FLT_MIN_10_EXP__ (-37)
#define _CALL_AIXDESC 1
#define __INTMAX_TYPE__ long int
#define __GNUC_MINOR__ 0
#define __DBL_MAX_10_EXP__ 308
#define __LDBL_DENORM_MIN__ 4.9406564584124654e-324L
#define __PTRDIFF_TYPE__ long int
#define _ARCH_PPC64 1
#define __LDBL_MIN_10_EXP__ (-307)
#define _Bool _Bool
#define __LDBL_DIG__ 15
SPU
$ spu-gcc -x c -dM -E /dev/null
#define __DBL_MIN_EXP__ (-1021)
#define __FLT_MIN__ 1.17549435e-38F
#define __CHAR_BIT__ 8
#define __WCHAR_MAX__ 2147483647
#define __DBL_DENORM_MIN__ 4.9406564584124654e-324
#define __FLT_EVAL_METHOD__ 0
#define __DBL_MIN_10_EXP__ (-307)
#define __FINITE_MATH_ONLY__ 0
#define __GNUC_PATCHLEVEL__ 2
#define __SPU__ 1
#define __SHRT_MAX__ 32767
#define __LDBL_MAX__ 1.7976931348623157e+308L
#define __UINTMAX_TYPE__ long long unsigned int
#define __CHAR_UNSIGNED__ 1
#define __LDBL_MAX_EXP__ 1024
#define __SCHAR_MAX__ 127
#define vector vector
#define __USER_LABEL_PREFIX__
#define __STDC_HOSTED__ 1
#define __LDBL_HAS_INFINITY__ 1
#define __DBL_DIG__ 15
#define __FLT_EPSILON__ 1.19209290e-7F
#define __LDBL_MIN__ 2.2250738585072014e-308L
#define __DECIMAL_DIG__ 17
#define __LDBL_HAS_QUIET_NAN__ 1
#define __GNUC__ 4
#define __DBL_MAX__ 1.7976931348623157e+308
#define __DBL_HAS_INFINITY__ 1
#define __USING_SJLJ_EXCEPTIONS__ 1
#define __DBL_MAX_EXP__ 1024
#define __LONG_LONG_MAX__ 9223372036854775807LL
#define __GXX_ABI_VERSION 1002
#define __FLT_MIN_EXP__ (-125)
#define __DBL_MIN__ 2.2250738585072014e-308
#define __DBL_HAS_QUIET_NAN__ 1
#define __REGISTER_PREFIX__
#define __NO_INLINE__ 1
#define __FLT_MANT_DIG__ 24
#define __VERSION__ "4.0.2 (CELL 3-2, Apr 11 2006)"
#define __SIZE_TYPE__ long unsigned int
#define __ELF__ 1
#define __FLT_RADIX__ 2
#define __LDBL_EPSILON__ 2.2204460492503131e-16L
#define __vector __attribute__((spu_vector))
#define __FLT_HAS_QUIET_NAN__ 0
#define __FLT_MAX_10_EXP__ 38
#define __LONG_MAX__ 2147483647L
#define __FLT_HAS_INFINITY__ 0
#define __LDBL_MANT_DIG__ 53
#define __WCHAR_TYPE__ int
#define __FLT_DIG__ 6
#define __INT_MAX__ 2147483647
#define __FLT_MAX_EXP__ 129
#define __DBL_MANT_DIG__ 53
#define __WINT_TYPE__ unsigned int
#define __LDBL_MIN_EXP__ (-1021)
#define __LDBL_MAX_10_EXP__ 308
#define __DBL_EPSILON__ 2.2204460492503131e-16
#define __INTMAX_MAX__ 9223372036854775807LL
#define __FLT_DENORM_MIN__ 1.40129846e-45F
#define __FLT_MAX__ 6.80564693e+38F
#define __FLT_MIN_10_EXP__ (-37)
#define __INTMAX_TYPE__ long long int
#define __GNUC_MINOR__ 0
#define __DBL_MAX_10_EXP__ 308
#define __LDBL_DENORM_MIN__ 4.9406564584124654e-324L
#define __PTRDIFF_TYPE__ long int
#define __LDBL_MIN_10_EXP__ (-307)
#define __LDBL_DIG__ 15