Make clang-format understand more line comments.

Apparently one needs to set LangOptions.LineComment.

Before "//* */" got reformatted to "/ /* */" as the lexer was returning
the token sequence (slash, comment). This could also lead to weird other
stuff, e.g. for people that like to using comments like:
//****************

llvm-svn: 177720

clang/lib/Format/Format.cpp

@@ -1643,6 +1643,7 @@ LangOptions getFormattingLangOpts() {
   LangOptions LangOpts;
   LangOpts.CPlusPlus = 1;
   LangOpts.CPlusPlus11 = 1;
+  LangOpts.LineComment = 1;
   LangOpts.Bool = 1;
   LangOpts.ObjC1 = 1;
   LangOpts.ObjC2 = 1;

clang/unittests/Format/FormatTest.cpp

@@ -490,6 +490,7 @@ TEST_F(FormatTest, FormatsLabels) {
 //===----------------------------------------------------------------------===//
 
 TEST_F(FormatTest, UnderstandsSingleLineComments) {
+  verifyFormat("//* */");
   verifyFormat("// line 1\n"
                "// line 2\n"
                "void f() {}\n");