AVR-GCCがパスに入っている状況下で以下のコマンド。

avr-gcc -dM -E - < /dev/null

その結果：

#define AVR 1
#define __AVR 1
#define __AVR_2_BYTE_PC__ 1
#define __AVR_ARCH__ 2
#define __AVR__ 1
#define __CHAR_BIT__ 8
#define __DBL_DENORM_MIN__ 1.40129846e-45
#define __DBL_DIG__ 6
#define __DBL_EPSILON__ 1.19209290e-7
#define __DBL_HAS_DENORM__ 1
#define __DBL_HAS_INFINITY__ 1
#define __DBL_HAS_QUIET_NAN__ 1
#define __DBL_MANT_DIG__ 24
#define __DBL_MAX_10_EXP__ 38
#define __DBL_MAX_EXP__ 128
#define __DBL_MAX__ 3.40282347e+38
#define __DBL_MIN_10_EXP__ (-37)
#define __DBL_MIN_EXP__ (-125)
#define __DBL_MIN__ 1.17549435e-38
#define __DEC128_DEN__ 0.000000000000000000000000000000001E-6143DL
#define __DEC128_EPSILON__ 1E-33DL
#define __DEC128_MANT_DIG__ 34
#define __DEC128_MAX_EXP__ 6144
#define __DEC128_MAX__ 9.999999999999999999999999999999999E6144DL
#define __DEC128_MIN_EXP__ (-6143)
#define __DEC128_MIN__ 1E-6143DL
#define __DEC32_DEN__ 0.000001E-95DF
#define __DEC32_EPSILON__ 1E-6DF
#define __DEC32_MANT_DIG__ 7
#define __DEC32_MAX_EXP__ 96
#define __DEC32_MAX__ 9.999999E96DF
#define __DEC32_MIN_EXP__ (-95)
#define __DEC32_MIN__ 1E-95DF
#define __DEC64_DEN__ 0.000000000000001E-383DD
#define __DEC64_EPSILON__ 1E-15DD
#define __DEC64_MANT_DIG__ 16
#define __DEC64_MAX_EXP__ 384
#define __DEC64_MAX__ 9.999999999999999E384DD
#define __DEC64_MIN_EXP__ (-383)
#define __DEC64_MIN__ 1E-383DD
#define __DECIMAL_DIG__ 9
#define __DEC_EVAL_METHOD__ 2
#define __FINITE_MATH_ONLY__ 0
#define __FLT_DENORM_MIN__ 1.40129846e-45F
#define __FLT_DIG__ 6
#define __FLT_EPSILON__ 1.19209290e-7F
#define __FLT_EVAL_METHOD__ 0
#define __FLT_HAS_DENORM__ 1
#define __FLT_HAS_INFINITY__ 1
#define __FLT_HAS_QUIET_NAN__ 1
#define __FLT_MANT_DIG__ 24
#define __FLT_MAX_10_EXP__ 38
#define __FLT_MAX_EXP__ 128
#define __FLT_MAX__ 3.40282347e+38F
#define __FLT_MIN_10_EXP__ (-37)
#define __FLT_MIN_EXP__ (-125)
#define __FLT_MIN__ 1.17549435e-38F
#define __FLT_RADIX__ 2
#define __GNUC_GNU_INLINE__ 1
#define __GNUC_MINOR__ 3
#define __GNUC_PATCHLEVEL__ 0
#define __GNUC__ 4
#define __GXX_ABI_VERSION 1002
#define __INTMAX_MAX__ 9223372036854775807LL
#define __INTMAX_TYPE__ long long int
#define __INT_MAX__ 32767
#define __LDBL_DENORM_MIN__ 1.40129846e-45L
#define __LDBL_DIG__ 6
#define __LDBL_EPSILON__ 1.19209290e-7L
#define __LDBL_HAS_DENORM__ 1
#define __LDBL_HAS_INFINITY__ 1
#define __LDBL_HAS_QUIET_NAN__ 1
#define __LDBL_MANT_DIG__ 24
#define __LDBL_MAX_10_EXP__ 38
#define __LDBL_MAX_EXP__ 128
#define __LDBL_MAX__ 3.40282347e+38L
#define __LDBL_MIN_10_EXP__ (-37)
#define __LDBL_MIN_EXP__ (-125)
#define __LDBL_MIN__ 1.17549435e-38L
#define __LONG_LONG_MAX__ 9223372036854775807LL
#define __LONG_MAX__ 2147483647L
#define __NO_INLINE__ 1
#define __PTRDIFF_TYPE__ int
#define __REGISTER_PREFIX__ 
#define __SCHAR_MAX__ 127
#define __SHRT_MAX__ 32767
#define __SIZEOF_DOUBLE__ 4
#define __SIZEOF_FLOAT__ 4
#define __SIZEOF_INT__ 2
#define __SIZEOF_LONG_DOUBLE__ 4
#define __SIZEOF_LONG_LONG__ 8
#define __SIZEOF_LONG__ 4
#define __SIZEOF_POINTER__ 2
#define __SIZEOF_PTRDIFF_T__ 2
#define __SIZEOF_SHORT__ 2
#define __SIZEOF_SIZE_T__ 2
#define __SIZEOF_WCHAR_T__ 2
#define __SIZEOF_WINT_T__ 2
#define __SIZE_TYPE__ unsigned int
#define __STDC_HOSTED__ 1
#define __STDC__ 1
#define __UINTMAX_TYPE__ long long unsigned int
#define __USER_LABEL_PREFIX__ 
#define __USING_SJLJ_EXCEPTIONS__ 1
#define __VERSION__ "4.3.0"
#define __WCHAR_MAX__ 32767
#define __WCHAR_TYPE__ int
#define __WINT_TYPE__ unsigned int