Allow overriding SCM version info

If the build is from a non-repository, these functions will return empty. This
patch allows using defines to CMake to set version info such as
-DGIT_BRANCH=master.

src/common/CMakeLists.txt

@@ -22,6 +22,11 @@ add_custom_command(OUTPUT scm_rev.cpp
       -DTITLE_BAR_FORMAT_RUNNING=${TITLE_BAR_FORMAT_RUNNING}
       -DBUILD_TAG=${BUILD_TAG}
       -DBUILD_ID=${DISPLAY_VERSION}
+      -DGIT_REF_SPEC=${GIT_REF_SPEC}
+      -DGIT_REV=${GIT_REV}
+      -DGIT_DESC=${GIT_DESC}
+      -DGIT_BRANCH=${GIT_BRANCH}
+      -DBUILD_FULLNAME=${BUILD_FULLNAME}
       -DGIT_EXECUTABLE=${GIT_EXECUTABLE}
       -P ${CMAKE_SOURCE_DIR}/CMakeModules/GenerateSCMRev.cmake
     DEPENDS