Stop sb-sprof test from failing on FreeBSD 10.

setitimer with small intervals is broken on FreeBSD 10.
Enable building 32-bit SBCL on 64-bit FreeBSD.

Allow for ./make.sh --arch=x86 to work on x86-64.
Remove unused ldt.h includes from x86-64-*-os.c files.
Remove strange #defines from *-linux-os.c

#define function_name somethine_nonexisting
just before a function named function_name doesn't appear to make any
sense.