The m4 and bash completion items are usable and relevant
depending on the host system's configuration. So, we check for the
presence of the programs that these items depend on, and only install
them when those programs are found.
For the Valgrind suppression files, we don't install them on Windows as
Valgrind is currently not supported on Windows.
Als fix the path where the GDB helpers are installed, as the path is
incorrectly constructed.
This will fix the "install" stage when building on Visual Studio at
least as there are some post-install steps that are related to them,
which will make use of these programs.
https://bugzilla.gnome.org/show_bug.cgi?id=783270
915ab35e96