We quote each passed through argument, and escape quote chars in them.
For cases when the passed through argument ends with a backslash, this
fails though, since whatever is unescaping it doesn't seem to handle
double backslashes for escaping backslashes themselves.
This allows non-msys build systems to use the triplet prefixed
compiler frontends on windows.
Keep the old shell script version as well, for easier hackability
on unix platforms.
Martin Storsjö