MSVC cannot handle MinGW-esque /c/foo paths, convert them to C:/foo.
We cannot resolve other paths starting with / like /home/foo so leave
them as-is so the user gets an error/warning from the compiler/linker.
These paths are commonly found in pkg-config files generated using
Autotools inside MinGW/MSYS and MinGW/MSYS2 environments.
Currently this is only done for PkgConfigDependency.
This exposes the already existing UserStringArrayOption class through
the meson_options.txt. The intention is to provide a way for projects to
take list/array type arguments and validate that all of the elements in
that array are valid without using complex looping constructrs.
Escaping spaces with '\ ' is the only way that works with both
pkg-config and pkgconf, so quote that way and unquote inside Meson.
This should work on all platforms.
Also fix the unit test to do the same.
https://github.com/pkgconf/pkgconf/issues/153
https://github.com/mesonbuild/meson/pull/1406 had an incomplete fix
for this. The test case caught it.
Note: this still doesn't test that setting it in the cross-info works,
but it's the same codepath as via the environment so it should be ok.
Also add a test() that can be run on all platforms.
Currently unit tests are only run on Linux, so this was only testing the
Ninja backend. This change reveals that build-by-default was broken with
the Visual Studio backend.