Fix fallback fesetenv and feupdateenv on FE_NOMASK_ENV (bug 17088).

This patch fixes bug 17088, fallback fesetenv and feupdateenv not
giving an error for an FE_NOMASK_ENV argument when it requires traps
to be enabled.  (This is the bug tested for by test-fenv-return.c.)

Tested mips64 soft-float.

	[BZ #17088]
	* math/fesetenv.c (__fesetenv)
	[FE_NOMASK_ENV && FE_ALL_EXCEPT != 0]: Return 1 for FE_NOMASK_ENV.
	* math/feupdateenv.c (__feupdateenv)
	[FE_NOMASK_ENV && FE_ALL_EXCEPT != 0]: Likewise.