acinclude.m4 (LIBGFOR_CHECK_FOR_BROKEN_ISFINITE, [...]): Remove.

	* acinclude.m4 (LIBGFOR_CHECK_FOR_BROKEN_ISFINITE,
	LIBGFOR_CHECK_FOR_BROKEN_ISNAN,
	LIBGFOR_CHECK_FOR_BROKEN_FPCLASSIFY): Remove.
	* configure.ac: Remove above checks.
	* libgfortran.h: Define isnan, isinf, isfinite, isnormal and
	signbit in terms of the respective built-ins.
	* io/write_float.def (WRITE_FLOAT): Use signbit() instead of
	__builtin_signbit().
	* intrinsics/c99_functions.c (tgamma): Use isnan() instead of
	__builtin_isnan().
	* config.h.in: Regenerate.
	* configure: Regenerate.

From-SVN: r164119