Add a developer warning to ports using python:2.7

With hat:	portmgr
Differential Revision:	https://reviews.freebsd.org/D23757

Mk/Uses/python.mk

@@ -324,11 +324,13 @@ _PYTHON_TEST_DEP=	yes
 WARNING+=	"PYTHON_DEFAULT must be a version present in PYTHON2_DEFAULT or PYTHON3_DEFAULT, if you want more Python flavors, set BUILD_ALL_PYTHON_FLAVORS in your make.conf"
 .endif
 
-.if ${_PYTHON_ARGS} == "2"
+.if ${_PYTHON_ARGS} == 2.7
+DEV_WARNING+=		"lang/python27 reached End of Life and will be removed on 2020-12-31, consider converting to a modern version of python"
+.elif ${_PYTHON_ARGS} == 2
 DEV_ERROR+=		"USES=python:2 is no longer supported, use USES=python:2.7"
-.elif ${_PYTHON_ARGS} == "3"
+.elif ${_PYTHON_ARGS} == 3
 DEV_ERROR+=		"USES=python:3 is no longer supported, use USES=python:3.5+ or an appropriate version range"
-.endif  # ${_PYTHON_ARGS} == "2"
+.endif  # ${_PYTHON_ARGS} == 2.7
 
 _PYTHON_VERSION:=	${PYTHON_DEFAULT}