x86: Reinstate hand-written unwind info for unix64.S
x86: Reinstate hand-written unwind info for unix64.S

One more try to get default Darwin to work.

s1341/libffi,plicease/libffi,plicease/libffi,bgarrels/libffi,Distrotech/libffi,rth7680/libffi,joshtriplett/libffi,nmav/libffi,bgarrels/libffi,plicease/libffi,plicease/libffi,s1341/libffi,rth7680/libffi,nmav/libffi,rth7680/libffi,joshtriplett/libffi,bgarrels/libffi,biosbits/libffi,nmav/libffi,Distrotech/libffi,Pan7/libffi,s1341/libffi,biosbits/libffi,s1341/libffi,biosbits/libffi,joshtriplett/libffi,biosbits/libffi,Pan7/libffi,joshtriplett/libffi,nmav/libffi,Distrotech/libffi,bgarrels/libffi,Pan7/libffi,Pan7/libffi,Distrotech/libffi,rth7680/libffi