[PATCH v3] Add configure check for python program

[Joseph Myers]

This has caused "make check" in a run-built-tests=no cross-compilation 
environment (with build-many-glibcs.py) to fail with:

make[3]: *** No rule to make target '/scratch/jmyers/glibc-bot/build/glibcs/aarch64-linux-gnu/glibc/nptl//scratch/jmyers/glibc-bot/build/glibcs/aarch64-linux-gnu/glibc/nptl/test-mutexattr-printers', needed by 'tests'.  Stop.

https://sourceware.org/ml/libc-testresults/2016-q4/msg00062.html

(Commit 8ce8299f9458c7fee8554ecd4b97cc5eddba4e4c is the only change 
between this and the previous build that worked.)

-- 
Joseph S. Myers
joseph@codesourcery.com