PCH merge bootstrap failure on systems without flex

[David Edelsohn]

>>>>> Geoff Keating writes:

Geoff> I intentionally used flex.  I wasn't the first to introduce it into
Geoff> mainline, though; that honour goes to Tim Josling who added
Geoff> gcc/treelang/lex.l.  If I got the makefiles right, gengtype-lex.c
Geoff> should be pregenerated in the release tarball, just like the uses of
Geoff> bison.

	GCC CVS frequently includes pre-processed files and gcc_update
adjusts the timestamps so that one does not need the tool unless one is
modifying the source file.

David