[rfc] common location for plugins

[Matthias Klose]

For packages of GCC I would like to see a common location where plugins can be 
installed; currently a path to the plugin has to be given on the command line, 
which is likely to be different for different installations.  What about 
-fplugin=<name> (without the .so) meaning to search for the plugin in a default 
location like <gcclibdir>/plugins for the plugin? -fplugin=<name>.so could also 
be used, but maybe would be ambiguous looking in the current dir, or the plugin dir.

  Matthias