CMake: fix failing build due to unsupported CONCAT command (CMake version 2.8.12)

Thanks to "dan0nl" for reporting the issue.

Author: Lukas955

pkg/CMakeLists.txt

@@ -51,8 +51,7 @@ if (NOT CPACK_PACKAGE_CONTACT OR CPACK_PACKAGE_CONTACT STREQUAL "")
     if (GIT_USER_NAME AND GIT_USER_EMAIL)
         message(STATUS "Maintainer contact for packages is not specified "
             "- using a name and email from the git configuration")
-        string(CONCAT CPACK_PACKAGE_CONTACT
-            ${GIT_USER_NAME} " <" ${GIT_USER_EMAIL} ">")
+        set(CPACK_PACKAGE_CONTACT "${GIT_USER_NAME} <${GIT_USER_EMAIL}>")
     endif()
 endif()