build: check for python-config in configure

build: check for python-config in configure

Currently, configure succeeds when python is installed without its
development components, i.e. python-config and headers. The subsequent
make will fail when gcc cannot locate Python.h.

This patch fixes that behavior by throwing an error at configure-time if
python-config cannot be found.

Signed-off-by: Joel Savitz <joelsavitz@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>