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/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index b523497..be704a7 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -449,7 +449,7 @@
       case PSK_InBoundsConstantIndices:
         if (!GEP->hasAllConstantIndices())
           return V;
-        // fallthrough
+        LLVM_FALLTHROUGH;
       case PSK_InBounds:
         if (!GEP->isInBounds())
           return V;
@@ -848,7 +848,7 @@
       // virtual (or inline) interface to handle this though, so instead we make
       // the TrackingVH accessors guarantee that a client never sees this value.
 
-      // FALLTHROUGH
+      LLVM_FALLTHROUGH;
     case Weak:
       // Weak goes to the new value, which will unlink it from Old's list.
       Entry->operator=(New);