cmake: add timestamp into build info log (6089)

CMakeLists.txt

@@ -759,6 +759,12 @@ endif()
 # ========================== build platform ==========================
 status("")
 status("  Platform:")
+if(NOT CMAKE_VERSION VERSION_LESS 2.8.11 AND NOT BUILD_INFO_SKIP_TIMESTAMP)
+  string(TIMESTAMP TIMESTAMP "" UTC)
+  if(TIMESTAMP)
+    status("    Timestamp:"    ${TIMESTAMP})
+  endif()
+endif()
 status("    Host:"             ${CMAKE_HOST_SYSTEM_NAME} ${CMAKE_HOST_SYSTEM_VERSION} ${CMAKE_HOST_SYSTEM_PROCESSOR})
 if(CMAKE_CROSSCOMPILING)
   status("    Target:"         ${CMAKE_SYSTEM_NAME} ${CMAKE_SYSTEM_VERSION} ${CMAKE_SYSTEM_PROCESSOR})