More functions unavailable on some systems.

More functions unavailable on some systems.
* configure.in (AC_CHECK_FUNCS): Add ctermid, setpgid, setsid,
tcgetpgrp, tcsetpgrp, and waitpid to the list of functions to
check for.
* configure, scmconfig.h.in: Updated, using autoconf and autoheader.
* posix.c (scm_sys_ctermid, scm_sys_setpgid, scm_sys_setsid,
scm_sys_tcgetpgrp, scm_sys_tcsetpgrp, scm_sys_waitpid): Put the
bodies of these functions in "#ifdef HAVE_MUMBLE" clauses, with a
stub that signals an error as the #else.