Make GIT_REV safer for reuse in downstream packaging

Author: Wheeez

Makefile

@@ -344,7 +344,7 @@ endif
 # Add git version info
 USE_GIT=
 ifeq ($(wildcard .git),.git)
-  GIT_REV=$(shell git describe --tag)
+  GIT_REV=$(shell git describe --tag | sed -e 's/-/_/g')
   ifneq ($(GIT_REV),)
     VERSION:=$(GIT_REV)
     USE_GIT=1