GCC 4.6 missing plugin headers

[Alex Leach]

Hi,

I built and installed GCC 4.6.4 last night - on amd64 Linux 3.9.6 - and  
the installation was missing c-family/c-common.h from its plugin  
directory. This header is installed by 4.7 and 4.8 branches, and is  
included by other core plugin headers on 4.6, e.g. cp/cp-tree.h, which my  
plugin includes directly.

After copying c-common.h to the 4.6 installation's  
plugin/include/c-family/ directory, all is well; my plugin compiles and  
runs fine on GCC versions 4.6 to 4.8. So I've added a configure-time  
warning for GCC4.6, but I thought it would be better if it was just  
installed with `make install`.

Are there any further releases planned for the 4.6 branch? Would a patch  
be accepted for this? I've got the 4.6 branch checked out in git, but  
don't know exactly where an edit would be needed.. Are there any reasons  
why this header is not installed with 4.6?

Kind regards,
Alex