LoongArch: Provide fmin/fmax RTL pattern

LoongArch: Provide fmin/fmax RTL pattern

We already had smin/smax RTL pattern using fmin/fmax instruction.  But
for smin/smax, it's unspecified what will happen if either operand is
NaN.  So we would generate calls to libc fmin/fmax functions with
-fno-finite-math-only (the default for all optimization levels expect
-Ofast).

But, LoongArch fmin/fmax instruction is IEEE-754-2008 conformant so we
can also use the instruction for fmin/fmax pattern and avoid the library
function call.

gcc/ChangeLog:

	* config/loongarch/loongarch.md (fmax<mode>3): New RTL pattern.
	(fmin<mode>3): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/fmax-fmin.c: New test.