Fix build from an extracted grafx2-2.5.*-src.tgz

we check if we are in a GIT working tree and load revision
from version.c if we are not.

also includes grafx2-2.5*-src.tgz in artifacts

.gitlab-ci.yml

@@ -11,6 +11,7 @@ job_linux:
     artifacts:
         paths:
             - "*.zip"
+            - "*.tgz"
 
 job_win32:
     stage: build