I receive the same error with both GODI and OPAM. I remember this error from somewhere but I couldn't figure out how to resolve it. 

It's Darwin 11.2.0, 64-bit kernel and extensions are turned off on this system. I remember that I could compile this code on an x64 kernel. 

....

gcc -I../byterun -DCAML_NAME_SPACE -DNATIVE_CODE -DTARGET_amd64 -DSYS_macosx  -O -D_FILE_OFFSET_BITS=64 -D_REENTRANT -I/sw/include  -c -o signals_asm.o signals_asm.c

signals_asm.c: In function ‘segv_handler’:

signals_asm.c:206: error: ‘struct __darwin_mcontext64’ has no member named ‘ss’

signals_asm.c:206: error: ‘struct __darwin_mcontext64’ has no member named ‘ss’

signals_asm.c:206: error: ‘struct __darwin_mcontext64’ has no member named ‘ss’

signals_asm.c:206: error: ‘struct __darwin_mcontext64’ has no member named ‘ss’

signals_asm.c:206: error: ‘struct __darwin_mcontext64’ has no member named ‘ss’

signals_asm.c:211: error: ‘struct __darwin_mcontext64’ has no member named ‘ss’

signals_asm.c:212: error: ‘struct __darwin_mcontext64’ has no member named ‘ss’