Update the gcc git repo if it was already checked out
Use the same git repository for the gcc builds
Removed comment about source reverting
Removed unnecessary use of gcc_src macro
Delete existing build directory before building gcc

This should be optimized in a future commit. Don't remove
the build directory and just run make inside of it again (without
configure). This needs adjusting of the use of the path variable,
as well as separate build directories for the first and second
build of gcc.
Only create the linux kernel build dir, if it doesn't exist yet
Only configure binutils if it hasn't been build yet
Remove libc build directory before building it again