clang-format: Don't remove 'unknown' tokens.

In certain macros or incorrect string literals, the token stream can
contain 'unknown' tokens, e.g. a single backslash or a set of empty
ticks. clang-format simply treated them as whitespace and removed them
prior to this patch.

This fixes llvm.org/PR17215

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192490 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Format/TokenAnnotator.cpp b/lib/Format/TokenAnnotator.cpp
index 8754989..a564d52 100644
--- a/lib/Format/TokenAnnotator.cpp
+++ b/lib/Format/TokenAnnotator.cpp
@@ -525,7 +525,8 @@
 
     // Reset token type in case we have already looked at it and then recovered
     // from an error (e.g. failure to find the matching >).
-    if (CurrentToken != NULL && CurrentToken->Type != TT_LambdaLSquare)
+    if (CurrentToken != NULL && CurrentToken->Type != TT_LambdaLSquare &&
+        CurrentToken->Type != TT_ImplicitStringLiteral)
       CurrentToken->Type = TT_Unknown;
   }
 
@@ -1292,6 +1293,8 @@
                                          const FormatToken &Tok) {
   if (Tok.Tok.getIdentifierInfo() && Tok.Previous->Tok.getIdentifierInfo())
     return true; // Never ever merge two identifiers.
+  if (Tok.Previous->Type == TT_ImplicitStringLiteral)
+    return Tok.WhitespaceRange.getBegin() != Tok.WhitespaceRange.getEnd();
   if (Line.Type == LT_ObjCMethodDecl) {
     if (Tok.Previous->Type == TT_ObjCMethodSpecifier)
       return true;