Build libunwind before mingw-w64-libraries

When --unwindlib=libunwind is implicit, we need to build libunwind
to have a complete working C compiler too. Currently this is worked
around by initially creating a dummy, empty libunwind.a, but with
the current version of libcxx/libunwind, we can get rid of that
workaround if we build it as soon as possible.

build-all.sh

@@ -35,8 +35,8 @@ done
 ./build-mingw-w64.sh $PREFIX
 ./build-mingw-w64-tools.sh $PREFIX
 ./build-compiler-rt.sh $PREFIX
-./build-mingw-w64-libraries.sh $PREFIX
 ./build-libcxx.sh $PREFIX
+./build-mingw-w64-libraries.sh $PREFIX
 ./build-compiler-rt.sh $PREFIX --build-sanitizers
 ./build-libssp.sh $PREFIX
 ./build-openmp.sh $PREFIX