This patch removes the (undocumented) LIBGCC2_TF_CEXT target macro,
replacing it by -fbuilding-libgcc predefines (and thereby gets rid of
another LIBGCC2_LONG_DOUBLE_TYPE_SIZE conditional, though some more
patches are needed before that target macro can be eliminated).  This
macro indicated the suffix used on __builtin_huge_val,
__builtin_copysign, __builtin_fabs built-in function names to produce
the names for a given floating-point mode.

Predefines are added for all floating-point modes supported for
libgcc, not just TFmode.  These are fully accurate for modes
corresponding to float, double and long double.  For other modes, the
suffix for *constants* is determined by the targetm.c.mode_for_suffix
hook (the limit to two possible suffixes 'w' and 'q' being hardcoded
in various places).  This is in fact the suffix for built-in functions
as well where such functions exist.

* For i386, the *q functions always exist (whether or not TFmode is
  used for long double).  The *w functions never exist (but this
  doesn't matter for libgcc, since no i386 configuration treats XFmode
  as a supported scalar mode if long double is TFmode; if __float80
  were to be supported for 64-bit Android, properly such functions
  ought to be added).

* For ia64, the *q functions exist for non-HP-UX (under HP-UX, long
  double is TFmode, so they aren't needed).  The *w functions never
  exist.  This is an issue for this libgcc code for the XFmode complex
  functions in libgcc on HP-UX; as I understand it, right now those
  will accidentally be using TFmode versions of those three functions,
  so involving unnecessary conversions, while the sanity check on CEXT
  accidentally passes because all it tests is the sizes of the types.

Because of the lack of 'w' functions, the patch uses 'l' when the
constant suffix is 'w', matching what the existing libgcc code would
do for IA64 HP-UX in that case.

Ideally there would be generic code to create such built-in functions
for all supported floating-point types.  That may be something to
consider if support for TS 18661-3 (standard bindings for IEEE
754-2008, defining names such as _Float128, and function names such as
copysignf128) is added in future.

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

gcc:
	* system.h (LIBGCC2_TF_CEXT): Poison.
	* config/i386/cygming.h (LIBGCC2_TF_CEXT): Remove.
	* config/i386/darwin.h (LIBGCC2_TF_CEXT): Likewise.
	* config/i386/dragonfly.h (LIBGCC2_TF_CEXT): Likewise.
	* config/i386/freebsd.h (LIBGCC2_TF_CEXT): Likewise.
	* config/i386/gnu-user-common.h (LIBGCC2_TF_CEXT): Likewise.
	* config/i386/openbsdelf.h (LIBGCC2_TF_CEXT): Likewise.
	* config/i386/sol2.h (LIBGCC2_TF_CEXT): Likewise.
	* config/ia64/ia64.h (LIBGCC2_TF_CEXT): Likewise.
	* config/ia64/linux.h (LIBGCC2_TF_CEXT): Likewise.

gcc/c-family:
	* c-cppbuiltin.c (c_cpp_builtins): Define __LIBGCC_*_FUNC_EXT__
	for supported floating-point modes.

libgcc:
	* libgcc2.c (CEXT): Define using __LIBGCC_*_FUNC_EXT__.

From-SVN: r215368