In particular, fix extension module build failures when trying to use
32-bit-only installer Pythons on systems with Xcode 4 (currently
OS X 10.8, 10.7, and optionally 10.6).
* Backport 3.3.0 fixes to 2.7 branch (for release in 2.7.4)
* Since Xcode 4 removes ppc support, extension module builds now
check for ppc compiler support and by default remove ppc and
ppc64 archs when they are not available.
* Extension module builds now revert to using system installed
headers and libs (/usr and /System/Library) if the SDK used
to build the interpreter is not installed or has moved.
* Try to avoid building extension modules with deprecated
and problematic Apple llvm-gcc compiler. If original compiler
is not available, use clang instead by default.
Ned Deily