march-generic.c: Skip for -march in multilib options.

march-generic.c: Skip for -march in multilib options.

	* gcc.dg/march-generic.c: Skip for -march in multilib options.
	* gcc.target/i386/isa-9.c: Skip for -march other than
	-march=amdfam10 in multilib options.
	* gcc.target/i386/pr42589.c: Skip for -march other than
	-march=i486 in multilib options.
	* gcc.target/i386/sse-19.c: Add -march=x86-64 option and skip for
	other -march in multilib options.

From-SVN: r165882