Debugger: Always check for availability of python with GDB

Trying to avoid that round-trip on versions that are known to
not have it puts us on the mercy of detecting the version,
which is unreliable by nature, and bad in practice, as proven
by the recent MinGW builds.

Change-Id: I122eb03fe0ddcb193ed8d45e672564f7113b662f
Reviewed-by: Ray Donnelly <mingw.android@gmail.com>
Reviewed-by: hjk <hjk121@nokiamail.com>