Use CFLAGS_NO_SIMD in preference to varying lists of -mno-xxxx flags.
Go ahead and defined -D_STANDALONE for all targets (only strictly
needed for some architecture, but harmless on those it isn't required
for). Also add -msoft-float to all architectures uniformly rather
that higgley piggley like it is today.

Differential Revision: https://reviews.freebsd.org/D3496