This fixes building/installing into a relative path.
This avoids having to pass --build-arg CORES=n when building the docker images.
This matches how it is normally available in GCC.
gcc/libssp's configure script runs checks for flags that clang doesn't implement. We actually just need to set a few HAVE defines and compile the .c sources, so just check out this subdirectory using svn and build it using a custom makefile.
Martin Storsjö