Log Message:
Pullup ticket #6056 - requested by maya
devel/glibmm: build fix

Revisions pulled up:
- devel/glibmm/buildlink3.mk                                    1.18

---
   Module Name:	pkgsrc
   Committed By:	maya
   Date:		Mon Sep  9 11:40:16 UTC 2019

   Modified Files:
   	pkgsrc/devel/glibmm: buildlink3.mk

   Log Message:
   glibmm: sync GCC_REQD between bl3, Makefile.

   Fixes atkmm builds with GCC < 4.9