Enabling ZSTD_TRACE leaves behind undefined weak symbols, which causes a
problem for gcc builds. The bfd linker emits an obscure error about
overlapping FDEs. We don't need ZSTD_TRACE for libsa, so just disable
it.
Also disable BMI2 instruction optimizations. The addition of the
optional BMI2 code paths caused the boot loader binaries to grow larger
(28 KiB for clang, 32 KiB for gcc). The boot loader binaries are size
constrained, and this pushed the gcc-generated lua_loader.bin over the
500000 byte limit, and the clang one to within 4k of the limit.
Fixes: 8a62a2a5659d ("zfs: merge openzfs/zfs@f8e5af53e")