The prl conversion script contrib/qt/convert-rpl-libs-to-cmake.pl
determines the library installation directory as being the given library
directory.
While this is true in most cases, it fails with plugins libraries which
are located in their own subtree.
This diff adds a new argument to the perl script so the caller can set
the library directory.
Also adds some quotes surrounding the paths to avoid dealing with issues
with spaces.
Depends on D2947.