[plugins-ici-cloning-instrumentation] install-plugin Makefile target

[Joern Rennecke]

Quoting Basile STARYNKEVITCH <basile@starynkevitch.net>:
> The interesting question is: do we have an installed plugins   
> directory? (We might have already discussed that, I forgot
> the details and the context, probably more than a year ago). I wish   
> we had one:

At the moment we have a directory for plugin header files, which is a  
subdirectory of an otherwise empty plugin directory:

[amylaar@laria gcc]$ /user/inria/bin/gcc --print-file-name=libgcc.a
/user/inria/lib/gcc/i686-pc-linux-gnu/4.5.0/libgcc.a
[amylaar@laria gcc]$ /user/inria/bin/gcc --print-file-name=plugin
/user/inria/lib/gcc/i686-pc-linux-gnu/4.5.0/plugin
[amylaar@laria gcc]$ ls -l `!!`
ls -l `/user/inria/bin/gcc --print-file-name=plugin`
total 4
drwxrwxr-x. 7 amylaar amylaar 4096 2009-11-18 17:48 include
[amylaar@laria gcc]$ /user/inria/bin/gcc --version
gcc (GCC) 4.5.0 20091108 (experimental)
Copyright (C) 2009 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.