PR fortran/48979

	* simplify.c (gfc_simplify_atan): Use mpfr_zero_p to check for zeros.
	(gfc_simplify_log): Likewise.
	(gfc_simplify_scale): Likewise.
	(gfc_simplify_exponent): Handle infinities and NaNs.
	(gfc_simplify_fraction): Handle infinities.
	(gfc_simplify_rrspacing): Handle signed zeros and NaNs.
	(gfc_simplify_set_exponent): Handle infinities and NaNs.
	(gfc_simplify_spacing): Handle zeros, infinities and NaNs.

	* gfortran.dg/ieee/intrinsics_1.f90: New test.

From-SVN: r216120