configure uses incorrect link order when testing libpython

configure uses incorrect link order when testing libpython

References:

https://stackoverflow.com/a/49868387
https://sourceware.org/bugzilla/show_bug.cgi?id=11420

Configure uses "gcc -o conftest -g ... conftest.c -ldl -lncurses -lm -ldl
... -lpthread ... -lpython2.7" when deciding whether give libpython is
usable.

That of course is the wrong link order, and only works for shared libraries
(mostly by accident), and only on some systems.

gdb/ChangeLog:

	PR gdb/11420
	* configure.ac: Prepend libpython.
	* python/python-config.py: Likewise.
	* configure: Regenerate.