help for old extension, first_last_agg bug in install with pg9.5

The C implementation is simple, the problem is with the makefile,
https://github.com/wulczer/first_last_agg/issues/2

*some clues?*

- - -

make
Makefile:25: /usr/lib/postgresql/9.5/lib/pgxs/src/makefiles/pgxs.mk:
No such file or directory
make: *** No rule to make target
`/usr/lib/postgresql/9.5/lib/pgxs/src/makefiles/pgxs.mk'.
Stop.

Using UBUNTU 14 LTS

See also https://github.com/wulczer/first_last_agg/blob/master/Makefile