[Gimple] Simplify (trunc)fma ((extend)a, (extend)b, (extend)c) to IFN_FMA (a,b, c).

[Gimple] Simplify (trunc)fma ((extend)a, (extend)b, (extend)c) to IFN_FMA (a,b, c).

a, b, c are same type as truncation type and has less precision than
extend type, the optimization is guarded under
flag_unsafe_math_optimizations.

gcc/ChangeLog:
	PR target/102464
	* match.pd: Simplify
	(trunc)fma ((extend)a, (extend)b, (extend)c) to IFN_FMA (a, b,
	c) under flag_unsafe_math_optimizations.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr102464-fma.c: New test.