[Clang][Win][JSC] dfg/DFGJITCode.h(163,18): warning: unqualified friend declaration referring to type outside of the nearest enclosing namespace is a Microsoft extension

clang-cl reports the following 2 warnings.

[1235/6540] Building CXX object Source\JavaScriptCore\CMakeFiles\JavaScriptCore.dir\__\__\JavaScriptCore\DerivedSources\unified-sources\UnifiedSource-f0a787a9-11.cpp.obj
In file included from C:\home\webkit\gc\WebKitBuild\Debug\JavaScriptCore\DerivedSources\unified-sources\UnifiedSource-f0a787a9-11.cpp:2:
In file included from C:\home\webkit\gc\Source\JavaScriptCore\bytecode/Repatch.cpp:34:
In file included from C:\home\webkit\gc\Source\JavaScriptCore\dfg\DFGSpeculativeJIT.h:31:
In file included from C:\home\webkit\gc\Source\JavaScriptCore\dfg/DFGAbstractInterpreter.h:31:
In file included from C:\home\webkit\gc\Source\JavaScriptCore\dfg/DFGGraph.h:37:
In file included from C:\home\webkit\gc\Source\JavaScriptCore\dfg/DFGPlan.h:35:
C:\home\webkit\gc\Source\JavaScriptCore\dfg/DFGJITCode.h(163,18): warning: unqualified friend declaration referring to type outside of the nearest enclosing namespace is a Microsoft extension; add a nested name specifier [-Wmicrosoft-unqualified-friend]
    friend class LLIntOffsetsExtractor;
                 ^
                 ::JSC::
In file included from C:\home\webkit\gc\WebKitBuild\Debug\JavaScriptCore\DerivedSources\unified-sources\UnifiedSource-f0a787a9-11.cpp:2:
In file included from C:\home\webkit\gc\Source\JavaScriptCore\bytecode/Repatch.cpp:34:
C:\home\webkit\gc\Source\JavaScriptCore\dfg\DFGSpeculativeJIT.h(1032,5): warning: non-void function does not return a value [-Wreturn-type]
    }
    ^
2 warnings generated.