Building without posix

[Dmitry Dzhus]

Is POSIX module considered optional?

Configuring guile-2.0 and git trunk with --disable-posix results in the
following error on my x86:

make  all-am
make[3]: Entering directory `/home/sphinx/projects/trunks/guile/libguile'
  [... skipped .lo lines ...]
  CC     libguile_2.0_la-weaks.lo
  CC     dynl.lo
  CC     net_db.lo
  CC     socket.lo
  CC     regex-posix.lo
  CCLD   libguile-2.0.la
  CC     guile-guile.o
  CCLD   guile
./.libs/libguile-2.0.so: undefined reference to `scm_stat'
./.libs/libguile-2.0.so: undefined reference to `scm_i_locale_mutex'
./.libs/libguile-2.0.so: undefined reference to `scm_ttyname'
./.libs/libguile-2.0.so: undefined reference to `scm_canonicalize_path'
./.libs/libguile-2.0.so: undefined reference to `scm_i_relativize_path'
collect2: ld returned 1 exit status
make[3]: *** [guile] Error