Fix libm fegetenv namespace (bug 17748).

Fix libm fegetenv namespace (bug 17748).

Some C90 libm functions call fegetenv via libc_feholdsetround*
functions in math_private.h.  This patch makes them call __fegetenv
instead, making fegetenv into a weak alias for __fegetenv as needed.

Tested for x86_64 (testsuite, and that disassembly of installed shared
libraries is unchanged by the patch).  Also tested for ARM
(soft-float) that fegetenv failures disappear from the linknamespace
test failures (however, similar fixes will also be needed for
fegetround, feholdexcept, fesetenv, fesetround and feupdateenv before
this set of namespace issues covered by bug 17748 is fully fixed and
those linknamespace tests start passing).

	[BZ #17748]
	* include/fenv.h (__fegetenv): Use libm_hidden_proto.
	* math/fegetenv.c (__fegetenv): Use libm_hidden_def.
	* sysdeps/aarch64/fpu/fegetenv.c (fegetenv): Rename to __fegetenv
	and define as weak alias of __fegetenv.  Use libm_hidden_weak.
	* sysdeps/alpha/fpu/fegetenv.c (__fegetenv): Use libm_hidden_def.
	* sysdeps/arm/fegetenv.c (fegetenv): Rename to __fegetenv and
	define as weak alias of __fegetenv.  Use libm_hidden_weak.
	* sysdeps/hppa/fpu/fegetenv.c (fegetenv): Likewise.
	* sysdeps/i386/fpu/fegetenv.c (__fegetenv): Use libm_hidden_def.
	* sysdeps/ia64/fpu/fegetenv.c (fegetenv): Rename to __fegetenv and
	define as weak alias of __fegetenv.  Use libm_hidden_weak.
	* sysdeps/m68k/fpu/fegetenv.c (__fegetenv): Use libm_hidden_def.
	* sysdeps/mips/fpu/fegetenv.c (fegetenv): Rename to __fegetenv and
	define as weak alias of __fegetenv.  Use libm_hidden_weak.
	* sysdeps/powerpc/fpu/fegetenv.c (__fegetenv): Use
	libm_hidden_def.
	* sysdeps/powerpc/nofpu/fegetenv.c (__fegetenv): Likewise.
	* sysdeps/powerpc/powerpc32/e500/nofpu/fegetenv.c (__fegetenv):
	Likewise.
	* sysdeps/s390/fpu/fegetenv.c (fegetenv): Rename to __fegetenv and
	define as weak alias of __fegetenv.  Use libm_hidden_weak.
	* sysdeps/sh/sh4/fpu/fegetenv.c (fegetenv): Likewise.
	* sysdeps/sparc/fpu/fegetenv.c (__fegetenv): Use libm_hidden_def.
	* sysdeps/tile/math_private.h (__fegetenv): New inline function.
	* sysdeps/x86_64/fpu/fegetenv.c (fegetenv): Rename to __fegetenv
	and define as weak alias of __fegetenv.  Use libm_hidden_weak.
	* sysdeps/generic/math_private.h (libc_feholdsetround_ctx): Use
	__fegetenv instead of fegetenv.
	(libc_feholdsetround_noex_ctx): Likewise.