Merge build-mingw-w64-widl.sh back into build-mingw-w64.sh

This allows checking out the mingw-w64 repo if it is missing, when
building widl.

build-cross-tools.sh

@@ -16,6 +16,6 @@ export HOST=$CROSS_ARCH-w64-mingw32
 
 ./build-llvm.sh $PREFIX
 ./strip-llvm.sh $PREFIX
-./build-mingw-w64-widl.sh $PREFIX --skip-triplet-prefix
+./build-mingw-w64.sh $PREFIX --skip-include-triplet-prefix
 ./install-wrappers.sh $PREFIX
 ./prepare-cross-toolchain.sh $NATIVE $PREFIX $CROSS_ARCH