Handle lines like (note the blank!):
# 1 "<command line>"
-- single-line line pragmas, of the form
-- # <line> "<file>" <extra-stuff> \n
<line_prag1> $digit+ { set_line line_prag1a }
-- single-line line pragmas, of the form
-- # <line> "<file>" <extra-stuff> \n
<line_prag1> $digit+ { set_line line_prag1a }
-<line_prag1a> \" $graphic* \" { set_file line_prag1b }
+<line_prag1a> \" [$graphic \ ]* \" { set_file line_prag1b }
<line_prag1b> .* { pop }
-- Haskell-style line pragmas, of the form
<line_prag1b> .* { pop }
-- Haskell-style line pragmas, of the form