lang/python3?: Fix python3.?-config behavior when symlinked

When python3.?-config is symlinked to another location it starts
outputting bogus paths.  For example

$ pwd
/home/tobias
$ python3.6-config --includes
-I/usr/local/include/python3.6m -I/usr/local/include/python3.6m
$ ln -s /usr/local/bin/python3.6-config python3-config
$ ./python3-config --includes
-I/home/include/python3.6m -I/home/include/python3.6m

This breaks ports trying to use BINARY_ALIAS together with
python3.?-config.  Apply a patch to resolve the symlink first before
trying to find the install prefix.

PR:		229749
Submitted by:	tobik
Reviewed by:	antoine, miwi
Approved by:	python (miwi)

lang/python37/Makefile

@@ -2,7 +2,7 @@
 # $FreeBSD$
 
 PORTNAME=	python
-PORTREVISION=	1
+PORTREVISION=	2
 PORTVERSION=	${PYTHON_PORTVERSION}
 CATEGORIES=	lang python ipv6
 MASTER_SITES=	PYTHON/ftp/python/${PORTVERSION}