i386-prefetch.exp: Skip tests when multilib flags contain -march.

	* gcc.misc-tests/i386-prefetch.exp: Skip tests when multilib flags
	contain -march.
	* gcc.dg/tree-ssa/prefetch-7.c, gcc.target/i386/387-1.c,
	gcc.target/i386/387-5.c, gcc.target/i386/cmov7.c,
	gcc.target/i386/funcspec-1.c, gcc.target/i386/funcspec-8.c,
	gcc.target/i386/gcc-have-sync-compare-and-swap-1.c,
	gcc.target/i386/gcc-have-sync-compare-and-swap-2.c,
	gcc.target/i386/isa-6.c, gcc.target/i386/lea.c,
	gcc.target/i386/pentium4-not-mull.c, gcc.target/i386/sse-5.c,
	gcc.target/i386/ssefn-1.c: Skip when multilib flags contain -march
	options other than that used in dg-options.

From-SVN: r151506