Remove the now-useless dependency on ufsread.c. In some cases, it was
on the wrong file. But in all cases, we now automatically generate
.depend files, so we don't need it explicitly.
Sponsored by: Netflix
simd / no float stuff is centeralized here. Also centralise
-ffreestanding since it is specified everywhere.
This, along with a change to share/mk/bsd.cpu.mk to include -mno-avx2
in CFLAGS_NO_SIMD should fix building for newer machines (eg with
CPUTYPE=haswell) where clang was generating avx2 instructions.
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