Do not use -Wpedantic with old Xcode gcc

Fixes: https://github.com/argtable/argtable3/issues/88

src/CMakeLists.txt

@@ -39,9 +39,12 @@ if(CMAKE_C_COMPILER_ID MATCHES "MSVC")
 else(CMAKE_C_COMPILER_ID MATCHES "GNU|Clang")
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c89")
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wconversion")
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wpedantic")
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wextra")
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall")
+  if ((CMAKE_C_COMPILER_ID MATCHES "GNU" AND CMAKE_C_COMPILER_VERSION VERSION_GREATER 4.2)
+    OR CMAKE_C_COMPILER_ID MATCHES "Clang")
+      set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wpedantic")
+  endif()
 endif()
 
 if(ARGTABLE3_ENABLE_ARG_REX_DEBUG)