cmake: Really add '--dirty' flag to 'git describe' for version

This fixes commit 2dc14b10de.

That commit added the '--dirty' argument the first time we generate the version
stamp file, which is when CMake produces the Makefiles (called from
awesomeConfig.cmake). Later on, we use build-utils/git-version-stamp.sh to
update this file. That file was missing this new argument to 'dit describe'

Signed-off-by: Uli Schlachter <psychon@znc.in>

build-utils/git-version-stamp.sh

@@ -13,7 +13,7 @@ die()
 }
 
 STAMP=`cat "$1" 2> /dev/null`
-CURRENT=`git describe 2>/dev/null`
+CURRENT=`git describe --dirty 2>/dev/null`
 
 if [ -z "$STAMP" -o -z "$CURRENT" ]
 then