* Adds new RetroArchQT build target to RetroArch_Metal.xcodeproj
Prerequisites:
* Install Qt Frameworks
$ brew install qt
* Build `moc` files using
$ make -f Makefile.apple HAVE_QT=1 Q=/usr/local/opt/qt/bin/moc generate
Limitations:
* Qt frameworks are not embedded in bundle, therefore Qt must be
installed via the `brew` command
* OSD message background
* clear glui background
* add Metal to configuration
* added optional config to compile Metal build without OpenGL
* fixed fill_pathname_join_delim; if out_path and dir are same, don't
strlcpy, as the results are undefined.