Merge pull request #7408 from hughbe/llvm-fallthrough

Use relatively new LLVM_FALLLTHROUGH instead of our own SWIFT_FALLTHROUGH

lib/Sema/CSApply.cpp

@@ -24,6 +24,7 @@
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/Support/Compiler.h"
 #include "llvm/Support/SaveAndRestore.h"
 
 using namespace swift;
@@ -2523,7 +2524,7 @@ namespace {
         }
 
         // Fall through to build the member reference.
-        SWIFT_FALLTHROUGH;
+        LLVM_FALLTHROUGH;
       }
 
       case OverloadChoiceKind::Decl: