fix gdb+python build failure if using non-GNU sed

fix gdb+python build failure if using non-GNU sed

Non-GNU sed do not like the '?' quantifier when used in a s/// regexp
that involve back-references, causing the build to fail when trying
to link with Python support. This fixes it by using the '*' quantifier
instead.

gdb/ChangeLog:

 	* configure.ac: Work around non-GNU sed limitation when computing
 	python version number.
 	* configure: Regenerate.