re PR rtl-optimization/10764 (ICE when using log(), -fast-math and optimization)

	PR optimization/10764
	* config/i386/i386.md (atan2df3, atan2sf3, atan2xf3, atan2tf3):
	Add an explicit clobber to show that UNSPEC_FPATAN clobbers st(1).
	(*fyl2x_sfxf3, *fyl2x_dfxf3, *fyl2x_xf3, *fyl2x_tfxf3):  Likewise,
	add an explicit clobber to show that UNSPEC_FYL2X clobbers st(1).
	(logsf2, logdf2, logxf2, logtf2): Update expander patterns to match
	the corresponding *fyl2x_?fxf3 instructions.

	* gcc.dg/builtins-15.c: New test case.

From-SVN: r66811