Tracking the line number by hand is error-prone since you need to
increment it in every \n matching pattern.

If '%option yylineno' is set, flex defines 'yylineno' to contain the
current line number and automatically updates it each time it reads a
\n character.  This is much more convenient although the lexer does
not initializes yylineno, so you need to set it to 1 each time you
start reading a new file, and restore it you go back to the previous
file.

I tested this with DEBUG_PARSE, and confirmed the same dump message
was produced.

I removed the perf-report option.  Otherwise, I see the following
message:
  %option yylineno entails a performance penalty ONLY on rules that
  can match newline characters

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>