As mingw-w64 now provides these routines, we no longer need to build
the original library from GCC.
As building with -fstack-protector-strong still links with -lssp
(and -lssp_nonshared), we still need to provide libraries with these
names, but they can be empty dummy libraries.
Building this tool requires having a full LLVM build available;
either by installing without LLVM_INSTALL_TOOLCHAIN_ONLY (and not
stripping the llvm installation yet) or by pointing it at the
LLVM build directory instead. The latter works better for our
normal build flows.
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.
Dmitry Tretyakov