Makefile.am: add missing $(EXEEXT)
Makefile.am: add missing $(EXEEXT)

This was presumably already needed back in isl-0.07-222-g1157635374
(add extract_interface for constructing interfaces to other languages,
Tue Aug 2 12:58:48 2011 +0200), but is has definitely been needed
since isl-0.18-1052-g5e4f4d395f (move bindings generation
to the top level, Fri Jan 26 15:55:13 2018 +0100)
as the top level has no way of knowing how extract_interface
is being built.

Signed-off-by: Sven Verdoolaege <235c10dd23b819f81cdc9756a251746bc184cab6@gmail.com>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl