Replace "fallthrough" comments with LLVM_FALLTHROUGH

This is a mechanical change of comments in switches like fallthrough,
fall-through, or fall-thru to use the LLVM_FALLTHROUGH macro instead.

llvm-svn: 278902
diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 39b472f..6c72cc1 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -3575,7 +3575,8 @@
                    Op.getOperand(0) == Op.getOperand(1))
             Op2Not = true;
         }
-        }  // fallthrough
+        LLVM_FALLTHROUGH;
+      }
       case PPC::BC:
       case PPC::BCn:
       case PPC::SELECT_I4: