set working dir of GitVersion to source dir; this helps with out of source builds

Author: Karl Herbig

dev/cmake/GitVersion.cmake

@@ -36,7 +36,9 @@ function(GetGitVersion _prefix)
 
   if(GIT_FOUND)
     execute_process(COMMAND ${GIT_EXECUTABLE} describe 
-      RESULT_VARIABLE ret OUTPUT_VARIABLE str OUTPUT_STRIP_TRAILING_WHITESPACE 
+      WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
+      RESULT_VARIABLE ret 
+      OUTPUT_VARIABLE str OUTPUT_STRIP_TRAILING_WHITESPACE 
       ERROR_QUIET)
   endif()