python: added configure args for distutils path detection

python: added configure args for distutils path detection

python-package.mk now defines (extends) CONFIGURE_ARGS that are
adjusting PREFIX and EXEC_PREFIX in distutils.sysconfig during
compilation. These variables are sometimes used by autotools to detect
path to Python header files. Adding these variables to python-package.mk
fixes compilation of legacy autotools-configured packages that already
include python-package.mk and do not overwrite CONFIGURE_ARGS.

Signed-off-by: Jan Čermák <redacted>
Cc: Alexandru Ardelean <redacted>