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/ARM/ARMAsmPrinter.cpp b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
index e2d3821..53b2c3d 100644
--- a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
+++ b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
@@ -249,7 +249,7 @@
           << "]";
         return false;
       }
-      // Fallthrough
+      LLVM_FALLTHROUGH;
     case 'c': // Don't print "#" before an immediate operand.
       if (!MI->getOperand(OpNum).isImm())
         return true;