(regopt): Take tmp buffer as additional argument.
(environ_init): Alllcate tmpbuf earlier. Use as temporary buffer in
call to regopt.
* tls_pbuf.cc (tmp_pathbuf::c_get): Allocate one additional char.
(tmp_pathbuf::w_get): Allocate one additional WCHAR.
* winf.cc (av::unshift): Use tmp_pathbuf to allocate buffer.
differently from those which are mounted with -X. Pass extra argument to
linebuf::fromargv.
* winf.h (MAXCYGWINCMDLEN): New define.
(linebuf::finish): Add a new argument denoting when command line overflow is
ok.
(linebuf::fromargv): Ditto.
* winf.cc (linebuf::finish): Implement above change.
(linebuf::fromargv): Ditto.