Problems when compiling for FreeBSD

1. Output of 'uname -m' on FreeBSD 14.1 is amd64 and not x86_64. So now path in src/ is wrong.
2. C compiler could not find arch-specific files. I added src/${ARCH} to include path.
3. gmake fails with error 255 on test_bootstrap because FreeBSD.s doesn't include abort.ns
and signals.ns. I replaced includes from FreeBSD.s with ones from Linux.s

Now it compiles.