TS 18661-1 defines <limits.h> and <stdint.h> macros for widths of
standard integer types and the typedefs defined in, or whose limits
are defined in, <stdint.h>.  (The connection to the main
floating-point subject matter of TS 18661-1 is that these are intended
to be used with the fromfp functions to convert from floating point to
integer types of any width in any rounding direction, though these
macros may be of more general use.)

This patch implements support for these macros in GCC's <limits.h> and
<stdint.h>.  To avoid needing to implement fixincludes for system
headers where GCC wraps the system libc's <stdint.h> in hosted mode,
the test for the <stdint.h> macros uses -ffreestanding (I'll add the
macros to glibc's headers separately) - but as usual for new features
in these headers, platforms (primarily OpenBSD) that use USER_H to
avoid using GCC's headers at all will have failures until the system
headers have the feature added or appropriate fixincludes are
implemented.

The header macros are implemented using appropriate new predefined
macros, with the code avoiding defining more such macros than
necessary (so one predefined macro suffices for corresponding signed
and unsigned types, while no such predefined macros are needed for the
exact-width types such as int8_t).

Bootstrapped with no regressions on x86_64-pc-linux-gnu.

gcc:
	* doc/cpp.texi (__SCHAR_WIDTH__, __SHRT_WIDTH__, __INT_WIDTH__)
	(__LONG_WIDTH__, __LONG_LONG_WIDTH__, __PTRDIFF_WIDTH__)
	(__SIG_ATOMIC_WIDTH__, __SIZE_WIDTH__, __WCHAR_WIDTH__)
	(__WINT_WIDTH__, __INT_LEAST8_WIDTH__, __INT_LEAST16_WIDTH__)
	(__INT_LEAST32_WIDTH__, __INT_LEAST64_WIDTH__)
	(__INT_FAST8_WIDTH__, __INT_FAST16_WIDTH__, __INT_FAST32_WIDTH__)
	(__INT_FAST64_WIDTH__, __INTPTR_WIDTH__, __INTMAX_WIDTH__):
	Document.
	* ginclude/stdint-gcc.h [__STDC_WANT_IEC_60559_BFP_EXT__]: Define
	width macros from TS 18661-1.
	* glimits.h [__STDC_WANT_IEC_60559_BFP_EXT__]: Likewise.

gcc/c-family:
	* c-cppbuiltin.c (builtin_define_type_width): New function.
	(builtin_define_stdint_macros, c_cpp_builtins): Define type width
	macros.

gcc/testsuite:
	* gcc.dg/limits-width-1.c, gcc.dg/stdint-width-1.c: New tests.

From-SVN: r240048