Fix parallel builds (make -jN) in SQL lexer/parser

Initial bug repport:
https://bugs.gentoo.org/show_bug.cgi?id=486434
Thanks to Patrick Lauer.

Problem is that generated parser.h is not ready when lexer.l is compiled.
See
https://www.gnu.org/software/automake/manual/html_node/Yacc-and-Lex.html
https://www.gnu.org/software/automake/manual/automake.html#Yacc-and-Lex