Makefile: ease dynamic-gettext-poison transition

Earlier we made the entire build to fail when GETTEXT_POISON=Yes is
given to make, to notify those who did not notice that text poisoning
is now a runtime behaviour.

It turns out that this is too irritating for those who need to build
and test different versions of Git that cross the boundary between
history with and without this topic to switch between two
environment variables.  Demote the error to a warning, so that you
can say something like

    make GETTEXT_POISON=Yes GIT_TEST_GETTEXT_POISON=Yes test

during the transition period, without having to worry about whether
exact version you are testing has or does not have this topic.

Signed-off-by: Junio C Hamano <[email protected]>
Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

Makefile

@@ -1447,7 +1447,7 @@ ifdef NO_SYMLINK_HEAD
 	BASIC_CFLAGS += -DNO_SYMLINK_HEAD
 endif
 ifdef GETTEXT_POISON
-$(error The GETTEXT_POISON option has been removed in favor of runtime GIT_TEST_GETTEXT_POISON. See t/README!)
+$(warning The GETTEXT_POISON option has been removed in favor of runtime GIT_TEST_GETTEXT_POISON. See t/README!)
 endif
 ifdef NO_GETTEXT
 	BASIC_CFLAGS += -DNO_GETTEXT