In these setups, we already install headers into prefix/include, in order to save diskspace.
When stripping via "install -s", install invokes the system's strip tool, which might not support the cross target that we are building for. This could also be handled by passing --strip-program=<arch>-w64-mingw32-strip to install though.
When cross compiling a llvm-mingw toolchain, we need to build widl for the intended host environment as well.