Added scripts applying GCC patches.

* gcc/jamfile: Added scripts applying GCC patches to GCC source trees.
* gcc/4.9.1.patch: A patch for GCC 4.9.1 source tree, which fixes
                   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62258
* gcc/4.8.3.patch: Likewise for GCC 4.8.3.