Do not prioritize our own libs over system libs.

This should fix the issue with macdeployqt not running due to failure to resolve symbols from libJPEG.dylib.

In a few cases, libraries we install to craftroot/lib may clash with system libraries. This is a well-known
problem with libjpeg, unfortunately, which MacOS will confuse with its own (same letters different case)
libJPEG.dylib. is not possible to give our libraries priority in such cases, as apps may legitimately link
against system libraries, directly or indirectly.

Rather, apps that _do_ need our version of any particular clashing lib will have to link against it statically.