MIPS BERI boot loader is built with -mno-abicalls and -fno-pic
so prevent adding PIE-related build flags.
Fix build after 9a227a2fd6 ("Enable PIE by default on 64-bit architectures")
Obtained from: Semihalf
Sponsored by: Stormshield
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.
Sponsored by: Netflix