[LLDB] Use LLVM_FALLTHROUGH instead of a custom comment

This fixes a warning when built with Clang in MinGW mode.

Differential Revision: https://reviews.llvm.org/D67860

llvm-svn: 372484

lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp

@@ -479,7 +479,7 @@ NativeProcessWindows::OnDebugException(bool first_chance,
       return ExceptionResult::BreakInDebugger;
     }
 
-    // Fall through
+    LLVM_FALLTHROUGH;
   default:
     LLDB_LOG(log,
              "Debugger thread reported exception {0:x} at address {1:x} "