Remove LLVM_C_FALLTHROUGH instances that cause warnings on clang-12 (#…

…6134)

The clang-12 warning is:

error: fallthrough annotation in unreachable code
[-Werror,-Wimplicit-fallthrough]

These LLVM_C_FALLTHROUGH were originally added to silence GCC warnings,
but the GCC PR validation build is has succeeded, so it looks like they
are not needed.

(cherry picked from commit eb4cec4)

tools/clang/lib/Sema/SemaCodeComplete.cpp

@@ -3063,18 +3063,15 @@ CXCursorKind clang::getCursorKindForDecl(const Decl *D) {
       switch (cast<ObjCPropertyImplDecl>(D)->getPropertyImplementation()) {
       case ObjCPropertyImplDecl::Dynamic:
         return CXCursor_ObjCDynamicDecl;
-        LLVM_C_FALLTHROUGH; //HLSL Change: avoid fallthrough warning
 
       case ObjCPropertyImplDecl::Synthesize:
         return CXCursor_ObjCSynthesizeDecl;
       }
 
       case Decl::Import:
         return CXCursor_ModuleImportDecl;
-        LLVM_C_FALLTHROUGH; //HLSL Change: avoid fallthrough warning
 
     case Decl::ObjCTypeParam:   return CXCursor_TemplateTypeParameter;
-    LLVM_C_FALLTHROUGH; //HLSL Change: avoid fallthrough warning
 
     default:
       if (const TagDecl *TD = dyn_cast<TagDecl>(D)) {