Fix dbl-64 atan2 in non-default rounding modes (bug 18210, bug 18211).

Fix dbl-64 atan2 in non-default rounding modes (bug 18210, bug 18211).

The dbl-64 implementation of atan2 does computations that expect to
run in round-to-nearest mode, and in other modes the errors can
accumulate to more than the maximum accepted 9ulp.  This patch makes
it use FE_TONEAREST internally, similar to other functions with such
issues.  Tests that previously produced large errors are added for
atan2 and the closely related carg, clog and clog10 functions.

Tested for x86_64 and x86 and ulps updated accordingly.

	[BZ #18210]
	[BZ #18211]
	* sysdeps/ieee754/dbl-64/e_atan2.c: Include <fenv.h>.
	(__ieee754_atan2): Set FE_TONEAREST mode for internal
	computations.
	* math/auto-libm-test-in: Add more tests of atan2, carg, clog and
	clog10.
	* math/auto-libm-test-out: Regenerated.
	* sysdeps/i386/fpu/libm-test-ulps: Update.
	* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.