[flang] Fix line continuation after bare labels (fm200.f)

[klausler]

Summary

Fixed-form line continuation was not working when the
preceding line was a bare label.

[klausler]

Rename function.

flang/lib/Parser/prescan.h

return p[0] == '/' && p[1] == '*' &&
                 features_.IsEnabled(
                     common::LanguageFeature::ClassicCComments)));
   }
 
   void LabelField(TokenSequence &, int outCol = 1);
   void SkipToEndOfLine();
   bool MustSkipToEndOfLine() const;
   void NextChar();
+  void SkipToNextSignificantCharacter();
   void SkipCComments();
   void SkipSpaces();
   static const char *SkipWhiteSpace(const char *);
   const char *SkipWhiteSpaceAndCComments(const char *) const;
   const char *SkipCComment(const char *) const;
   bool NextToken(TokenSequence &);
   bool ExponentAndKind(TokenSequence &);
   void QuotedCharacterLiteral(TokenSequence &, const char *start);

flang/lib/Parser/prescan.cpp

if (outCol == 1) {
       token.Put("      ", 6, sixSpaceProvenance_.start());
     } else {
       for (; outCol < 7; ++outCol) {
         token.PutNextTokenChar(' ', spaceProvenance_);
       }
       token.CloseToken();
     }
   }
+  SkipToNextSignificantCharacter();
 }
 
 void Prescanner::SkipToEndOfLine() {
   while (*at_ != '\n') {
     ++at_, ++column_;
   }
 }
 

 void Prescanner::NextChar() {
   CHECK(*at_ != '\n');
   ++at_, ++column_;
   while (at_[0] == '\xef' && at_[1] == '\xbb' && at_[2] == '\xbf') {
     // UTF-8 byte order mark - treat this file as UTF-8
     at_ += 3;
     encoding_ = Encoding::UTF_8;
   }
+  SkipToNextSignificantCharacter();
+}
+
+// Skip everything that should be ignored until the next significant
+// character is reached; handles C-style comments in preprocessing
+// directives, Fortran ! comments, stuff after the right margin in
+// fixed form, and all forms of line continuation.
+void Prescanner::SkipToNextSignificantCharacter() {
   if (inPreprocessorDirective_) {
     SkipCComments();
   } else {
     bool mightNeedSpace{false};
     if (MustSkipToEndOfLine()) {
       SkipToEndOfLine();
     } else {
       mightNeedSpace = *at_ == '\n';