Work around portability problem on Solaris 10: flex-generated

Work around portability problem on Solaris 10: flex-generated
files include <stdio.h> before <config.h>, which messes up
because the latter defines __EXTENSIONS__.  Address the problem
by creating two new little files that include <config.h> first,
then include the flex-generated files.  Rewrite everyone else
to include <config.h> first, as well.
* lib/timevar.c: Always include "config.h".
* src/Makefile.am (bison_SOURCES): Replace scan-gram.l with
scan-gram-c.c, and scan-skel.l with scan-skel-c.c.
(EXTRA_bison_SOURCES): New macro.
* src/scan-gram-c.c, src/scan-skel-c.c: New files.
* src/system.h: Don't include config.h.
* src/LR0.c: Include <config.h> first.
* src/assoc.c: Likewise.
* src/closure.c: Likewise.
* src/complain.c: Likewise.
* src/conflicts.c: Likewise.
* src/derives.c: Likewise.
* src/files.c: Likewise.
* src/getargs.c: Likewise.
* src/gram.c: Likewise.
* src/lalr.c: Likewise.
* src/location.c: Likewise.
* src/main.c: Likewise.
* src/muscle_tab.c: Likewise.
* src/nullable.c: Likewise.
* src/output.c: Likewise.
* src/parse-gram.y: Likewise.
* src/print.c: Likewise.
* src/print_graph.c: Likewise.
* src/reader.c: Likewise.
* src/reduce.c: Likewise.
* src/relation.c: Likewise.
* src/state.c: Likewise.
* src/symlist.c: Likewise.
* src/symtab.c: Likewise.
* src/tables.c: Likewise.
* src/uniqstr.c: Likewise.
* src/vcg.c: Likewise.