Fix version.c not found error.

Index: Makefile
--- Makefile.orig
+++ Makefile
@@ -57,7 +57,7 @@ ifeq (true,$(shell git rev-parse --is-inside-work-tree
   endif
 else
   # outside git repository : get version stored in version.c
-  GIT_REVISION := $(shell cat version.c | cut -f 2 -d '"')
+  GIT_REVISION := ""
 endif
 
   REVISION_CACHE = .revision.cache
