And actually test that prog.path() works. The earlier test was just
running the command without checking if it succeeded.
Also make everything use prog.get_command() or get_path() instead of
accessing the internal member prog.fullpath directly.
Instead of adding it everywhere manually, create a wrapper called
mesonlib.Popen_safe and use that everywhere that we call an executable
and extract its output.
This will also allow us to tweak it to do more/different things if
needed for some locales and/or systems.
Closes#1079
Instead of blindly searching in PATH, use
Qt5Dependency.compilers_detect() (same for qt4) to get moc/uic/rcc.
This is much more robust, and it improves the chances that the correct
ones will be found. We still manually verify for now because the
fallback in dependencies.py for searching is stll to look in PATH for
backwards-compat, and because people probably have setups like that.
Also sync the qt4 module with the qt5 module w.r.t. resource compilation
and make the compiled qrc.cpp file unique in terms of the framework
version used (4 vs 5). This is needed for the test to work properly,
which now covers both Qt4 and 5.
Without this a strange exception is spewed that no one would be able to
understand. Finding each of those compilers isn't a problem unless
sources are specified that require those compilers, so only error out in
those cases.
Closes#758
Nirbheek Chauhan