Pacify -DGNULIB_POSIXCHECK.

Pacify -DGNULIB_POSIXCHECK.

* bootstrap.conf (gnulib_modules): Add all modules suggested by
-DGNULIB_POSIXCHECK.
* src/files.c (file_name_split)
* src/getargs.c (getargs)
* src/location.c (boundary_set_from_string)
* src/output.c (token_definitions_output, output_skeleton)
* src/parse-gram.y (prologue_declaration)
* src/scan-gram.l (handle_syncline)
* src/symtab.c (symbol_new): Use mbschr and mbsrchr instead of
strchr and strrchr.  In the cases of command-line options, file
names, and thus locations, functionality may be improved.  In the
case of symbol names, there should be no functional difference as
all characters are ASCII, so the intended benefit is just warning
suppression.