Fix x86_64 -mfpmath=387 float_t, double_t (bug 20787).

Fix x86_64 -mfpmath=387 float_t, double_t (bug 20787).

Bug 20787 reports that, while float_t and double_t for 32-bit x86
properly respect -mfpmath=sse, for x86_64 they fail to reflect
-mfpmath=387, which is valid if unusual and results in FLT_EVAL_METHOD
being 2.  This patch fixes the definitions to respect
__FLT_EVAL_METHOD__ in that case, arranging for the test that the
types correspond with FLT_EVAL_METHOD to be run with both -mfpmath=387
and -mfpmath=sse.

Note: this patch will also have the effect of making float_t and
double_t be long double for x86_64 with -mfpmath=sse+387, when
FLT_EVAL_METHOD is -1.  It seems reasonable for x86_64 to be
consistent with 32-bit x86 in this case (and that definition is
conservatively safe, in that it makes the types correspond to the
widest evaluation format that might be used).

Tested for x86-64 and x86.

	[BZ #20787]
	* sysdeps/x86/bits/mathdef.h (float_t): Do not define to float if
	[__x86_64__] when __FLT_EVAL_METHOD__ is nonzero.
	(double_t): Do not define to double if [__x86_64__] when
	__FLT_EVAL_METHOD__ is nonzero.
	* sysdeps/x86/fpu/test-flt-eval-method-387.c: New file.
	* sysdeps/x86/fpu/test-flt-eval-method-sse.c: Likewise.
	* sysdeps/x86/fpu/Makefile [$(subdir) = math] (tests): Add
	test-flt-eval-method-387 and test-flt-eval-method-sse.
	[$(subdir) = math] (CFLAGS-test-flt-eval-method-387.c): New
	variable.
	[$(subdir) = math] (CFLAGS-test-flt-eval-method-sse.c): Likewise.