[PATCH v2 02/20] gcc-plugins: Detail c-common.h location for GCC 4.6

The c-common.h file moved in stock gcc 4.7, not gcc 4.6. However, most people building plugins with gcc 4.6 are using the Debian or Ubuntu version, which includes a patch to move the headers to the 4.7 location. In case anyone trips over this with a stock gcc 4.6, add a pointer to the patch used

[PATCH v2 02/20] gcc-plugins: Detail c-common.h location for GCC 4.6

The c-common.h file moved in stock gcc 4.7, not gcc 4.6. However, most people building plugins with gcc 4.6 are using the Debian or Ubuntu version, which includes a patch to move the headers to the 4.7 location. In case anyone trips over this with a stock gcc 4.6, add a pointer to the patch used