Removed -Wc++98-compat-extra-semi for compatibility with older clang.

Change-Id: I6dfadb5289a4396ad2f3d16baf1bdb99c7534174

CMakeLists.txt

@@ -193,7 +193,7 @@ elseif(${CMAKE_CXX_COMPILER_ID} MATCHES "Clang")
       "${CMAKE_CXX_FLAGS} -std=c++0x -Wall -pedantic -Werror -Wextra -Wno-unused-parameter")
   set(FLATBUFFERS_PRIVATE_CXX_FLAGS "-Wold-style-cast")
   if(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.8)
-    list(APPEND FLATBUFFERS_PRIVATE_CXX_FLAGS "-Wimplicit-fallthrough" "-Wextra-semi" "-Wc++98-compat-extra-semi" "-Werror=unused-private-field") # enable warning
+    list(APPEND FLATBUFFERS_PRIVATE_CXX_FLAGS "-Wimplicit-fallthrough" "-Wextra-semi" "-Werror=unused-private-field") # enable warning
   endif()
   if(FLATBUFFERS_LIBCXX_WITH_CLANG)
     if(NOT "${CMAKE_SYSTEM_NAME}" MATCHES "Linux")