PR target/30652
	PR middle-end/20558

	* builtins.c (expand_builtin_interclass_mathfn): Provide a
	generic fallback for isinf.
	* c-cppbuiltin.c (builtin_define_float_constants): Move FP max
	calculation code ...
	* real.c (get_max_float): ... to here.
	* real.h (get_max_float): New.

testsuite:
	* gcc.dg/pr28796-1.c: Add more cases.
	* gcc.dg/pr28796-2.c: Likewise.

From-SVN: r126724