Disable python support for gdb-7.x

Before python is also prebuilt, disable python support in gdb-7.x
for now, otherwise gdb-7.x/configure may pick up whatever python
in host and build gdb with hard-wired dependency to specific version
of python.

See related issue:
  http://code.google.com/p/android/issues/detail?id=36120

Change-Id: I15d1144767343fb717864470f7a57f66fd7ba127