x86: Don't issue vzeroupper if callee returns AVX register

x86: Don't issue vzeroupper if callee returns AVX register

Don't issue vzeroupper before function call if callee returns AVX
register since callee must be compiled with AVX.

gcc/

	PR target/101495
	* config/i386/i386.c (ix86_check_avx_upper_stores): Moved before
	ix86_avx_u128_mode_needed.
	(ix86_avx_u128_mode_needed): Return AVX_U128_DIRTY if callee
	returns AVX register.

gcc/testsuite/

	PR target/101495
	* gcc.target/i386/avx-vzeroupper-28.c: New test.