Fix generation of the version.h header when inside a Git submodule.

doc/changelog.dox

@@ -89,6 +89,8 @@ See also:
     assumed macOS is always desktop GL (see [mosra/magnum#452](https://github.com/mosra/magnum/issues/452))
 -   Avoiding conflicts of Magnum's own GL headers with `GLES3/gl32.h` (see
     [mosra/magnum#460](https://github.com/mosra/magnum/issues/460))
+-   The `version.h` header now gets populated from Git correctly also when
+    inside a CMake subproject
 
 @subsection changelog-latest-bugfixes Bug fixes
 

src/Magnum/CMakeLists.txt

@@ -37,6 +37,9 @@ if(Git_FOUND)
     execute_process(COMMAND ${GIT_EXECUTABLE} describe --match "v*" --long
         OUTPUT_VARIABLE MAGNUM_VERSION_STRING
         RESULT_VARIABLE _MAGNUM_VERSION_RESULT
+        # Otherwise this gets executed in the build dir, which might be inside
+        # a totally different Git working copy
+        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
         ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
     if(MAGNUM_VERSION_STRING MATCHES "^v([0-9][0-9][0-9][0-9])\\.0?([0-9][0-9]?)-([0-9]+)-g([a-f0-9]+)$")
         set(MAGNUM_VERSION_YEAR ${CMAKE_MATCH_1})