Copied sys-devel/gcc from toolchain overlay

That is for tracking changes from original.
Added gcc-4.9.0_pre99990002 - Concept Lite 0.2

For additional information check:
http://concepts.axiomatics.org/%CB%9Cans/
http://isocpp.org/blog/2013/03/new-paper-n3580-concepts-lite-andrew-sutton-bjarne-stroustrup-gabriel-dos-r
http://isocpp.org/files/papers/n3580.pdf