python: avoid failures due to $(am__py_compile) being undefined

python: avoid failures due to $(am__py_compile) being undefined

Fixes automake bug#10995, introduced in commit v1.11-372-gb46debf.

* lib/am/python.am: Move the definition of 'am__py_compile' to
ensure it is always emitted in the output Makefile.in.  Previously,
this wouldn't have happened if the input Makefile.am contained a
'noinst_PYTHON' declaration before a 'python_PYTHON' one.
* tests/Makefile.am (XFAIL_TESTS): Remove 'python-pr10995.test' and
'python.test'.
* NEWS: Update.

Copyright-paperwork-exempt: yes
Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>