* Adds GCC 4.0 version info to --config output.
* Splits gcc_build into gcc_40_build and gcc_42_build.
* Adds alias gcc_build to gcc_42_build for compatibility.
* Updates Xcode checking to also check GCC 4.0 version.

These changes are a combination of work by AdamV and my work
on my Tiger branch. This information would be useful for all
installs since some formulae compile with GCC 4.0.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>