Added LLVM_FALLTHROUGH to address gcc warning: this statement may fall through.

llvm-svn: 303585
diff --git a/llvm/lib/Support/GraphWriter.cpp b/llvm/lib/Support/GraphWriter.cpp
index d0e1d50..f70b77d 100644
--- a/llvm/lib/Support/GraphWriter.cpp
+++ b/llvm/lib/Support/GraphWriter.cpp
@@ -43,6 +43,7 @@
             Str.erase(Str.begin()+i); continue;
           default: break;
         }
+        LLVM_FALLTHROUGH;
     case '{': case '}':
     case '<': case '>':
     case '|': case '"':