Fix -j builds for gcc-3.4. The .nx build in cc_tools was breaking

Fix -j builds for gcc-3.4.  The .nx build in cc_tools was breaking
parallelism because individual source/header dependancies were being built
in parallel, and this was causing the helper programs to build in parallel
and/or generate the same header file in parallel.

Remove all direct dependancies on the helper programs.  Make libgcc
dependant on cc_tools (to generate required header files), clean up
the dependancy target for cc_tools, and force make depend to build
the tools.  This should result in all the tools being available to the
rest of the gcc-3.4 build.

Tested with several -j 8 builds.  There could still be additional
-j issues.