Integrate gcc 3.4.2 and add patches from both openembedded (6??-*)

  and Dan Kegel's crosstools (7??-*).
Use makefile vars for toolchain names in ccache.mk and gdb.mk.
Fix a g++-related symlink issue with ccache.
Change the default to gcc 3.4.2 and binutils 2.15.91.0.2 (now that mips
is building).  Let the users go forth and test...  ;-)