Use "gmake" instead of "make" when gmake is available.
The makefile used for libssp is a handwritten one that requires
GNU make features. mingw-w64 uses automake, which in principle should
work with BSD make, but mingw-w64-headers hangs indefinitely if built
with BSD make.
For build-mingw-w64.sh to succeed when installing to such a path,
the mingw-w64 version has to be updated to the latest git master.
build-mingw-w64-libraries.sh still fails in this case, as libtool
fails to properly quote $LD in a test for whether the linker is GNU ld.
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