PGXS "check" target forcing an install ?

I've noted that upgrading from PostgreSQL 9.3 to 9.5 I'm suddenly
unable to specify a "check" rule in the Makefile that includes the
PGXS one. The error is:
$ make checkrm -rf ''/tmp_installmake -C '/home/postgresql-9.5/lib/pgxs/src/makefiles/../..' DESTDIR=''/tmp_install
installmake[1]:Entering directory `/home/postgresql-9.5/lib/pgxs'make[1]: *** No rule to make target `install'.
Stop.make[1]:Leaving directory `/home/postgresql-9.5/lib/pgxs'make: *** [temp-install] Error 2
 

I tracked the dangerous -rf to come from Makefile.global and it's empty
string being due to abs_top_builddir not being define in my own Makefile.

But beside that, which I can probably fix, it doesn't sound correct
that a "check" rule insists in finding an "install" rule. I'm also
surprised that there's no warning coming out from the "make" invocation
given I'm defining a "check" rule myself (after inclusion).

Minimal Makefile reproducing the error:
 PGXS := /home/postgresql-9.3/lib/pgxs/src/makefiles/pgxs.mk # succeeds PGXS :=
/home/postgresql-9.5/lib/pgxs/src/makefiles/pgxs.mk# fails include $(PGXS) check:   echo "Checking"
 

To verify, just run "make check"

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