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/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 7dfff5b..bbbc51a 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -3748,7 +3748,7 @@
         ArgOffset += PtrByteSize;
         break;
       }
-      // FALLTHROUGH
+      LLVM_FALLTHROUGH;
     case MVT::i64:  // PPC64
       if (GPR_idx != Num_GPR_Regs) {
         unsigned VReg = MF.addLiveIn(GPR[GPR_idx], &PPC::G8RCRegClass);