[PATCH] Inline C99 math functions

[Wilco Dijkstra]

Add inlining of the C99 math functions isinf/isnan/signbit/isfinite/isnormal/fpclassify using GCC
built-ins when available. Since going through the PLT is expensive for these small functions,
inlining results in major speedups (about 7x on Cortex-A57 for isinf). The GCC built-ins are not
correct if signalling NaN support is required, and thus are turned off in that case (see GCC bug
66462). The test-snan.c tests sNaNs and so must be explicitly built with -fsignaling-nans.

As a result of this many target overrides and the various __isnan/__finite inlines in math_private.h
are no longer required. If agreed we could remove all this code and only keep the generic definition
of isinf/etc which will use the builtin.

Tested on AArch64. OK for commit?

ChangeLog: 
2015-06-15  Wilco Dijkstra  <wdijkstr@arm.com>

	* math/Makefile: Build test-snan.c with -fsignaling-nans.	
	* math/math.h (fpclassify): Use __builtin_fpclassify when
	available.  (signbit): Use __builtin_signbit(f/l).
	(isfinite): Use__builtin_isfinite.  (isnormal): Use
	__builtin_isnormal.  (isnan): Use __builtin_isnan.
	(isinf): Use __builtin_isinf_sign.

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