to be gcc's default before r198344, calls to atomic builtins will not be
expanded inline. Instead, they will be generated as calls to external
functions (e.g. __sync_fetch_and_add_N), leading to linking errors later
on.
Put in a seatbelt that disables use of atomic builtins in libstdc++ and
llvm, when tuning specifically for the real i386 CPU. This does not
protect against all possible issues, but it is better than nothing.
Even though it's nice to use posix_spawn() instead of manually using
fork()/exec(), it's better to disable this. FreeBSD 7 doesn't support
this interface. When enabled, we can't build tblgen, which prevents us
from building FreeBSD 9 on 7.
Tested by: raj
