Test gcc.target/arm/pr43698.c specifies -march=armv7-a and fails
execution for multilibs whose hardware or simulator doesn't support that
architecture.  The test doesn't depend on that option, and without it
will occasionally run for such a target anyway.  This patch removes the
option, letting it pass for all multilibs.

I don't yet have an FSF copyright assignment (it's currently in the
hands of the FSF) but this patch is small enough to not require one.  If
this is OK someone else will need to appy it.