Build a mingw32-make.exe when cross building toolchains

This can be used e.g. for building Qt without any MSYS installation,
and should also work for cmake, if using the mingw makefiles
generator.

build-cross-tools.sh

@@ -18,3 +18,4 @@ HOST=$CROSS_ARCH-w64-mingw32
 ./build-mingw-w64.sh $PREFIX --skip-include-triplet-prefix --host=$HOST
 ./install-wrappers.sh $PREFIX --host=$HOST
 ./prepare-cross-toolchain.sh $NATIVE $PREFIX $CROSS_ARCH
+./build-make.sh $PREFIX --host=$HOST