Clang: improve usefullness of clang-warnings

- don't check c++98 compatibility
 - don't show warnings on third-party code
 - don't check for padding

CMakeLists.txt

@@ -20,7 +20,7 @@ if( CMAKE_CXX_COMPILER_ID MATCHES "Clang" )
     set( CMAKE_C_FLAGS_RELEASE          "-O4 -DNDEBUG" )
     set( CMAKE_C_FLAGS_RELWITHDEBINFO   "-O2 -g" )
 
-    set( CMAKE_CXX_FLAGS                "${CMAKE_CXX_FLAGS} -Weverything" )
+    set( CMAKE_CXX_FLAGS                "${CMAKE_CXX_FLAGS} -Weverything -Wno-c++98-compat -Wno-padded" )
     set( CMAKE_CXX_FLAGS_DEBUG          "-g" )
     set( CMAKE_CXX_FLAGS_MINSIZEREL     "-Os -DNDEBUG" )
     set( CMAKE_CXX_FLAGS_RELEASE        "-O4 -DNDEBUG" )

thirdparty/CMakeLists.txt

@@ -1,3 +1,8 @@
+if( CMAKE_CXX_COMPILER_ID MATCHES "Clang" )
+    # Suppress warnings entirely; not interesting in third-party code
+    set( CMAKE_CXX_FLAGS                "${CMAKE_CXX_FLAGS} -w" )
+endif()
+
 if( WITH_CRASHREPORTER )
     macro( qt_wrap_ui )
         qt5_wrap_ui( ${ARGN} )