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)

1 files changed, 11 insertions, 0 deletions

diff --git a/lang/python37/files/patch-Misc__python-config.sh.in b/lang/python37/files/patch-Misc__python-config.sh.in
new file mode 100644
index 000000000000..ebb0c6a51f6d
--- /dev/null
+++ b/lang/python37/files/patch-Misc__python-config.sh.in
@@ -0,0 +1,11 @@
+--- Misc/python-config.sh.in.orig	2018-07-13 21:07:16 UTC
++++ Misc/python-config.sh.in
+@@ -15,7 +15,7 @@ fi
+ # Returns the actual prefix where this script was installed to.
+ installed_prefix ()
+ {
+-    RESULT=$(dirname $(cd $(dirname "$1") && pwd -P))
++    RESULT=$(dirname $(cd $(dirname $(realpath "$1")) && pwd -P))
+     if which readlink >/dev/null 2>&1 ; then
+         if readlink -f "$RESULT" >/dev/null 2>&1; then
+           RESULT=$(readlink -f "$RESULT")