When computing lispdir, don't load emacs site wide init file.

When computing lispdir, don't load emacs site wide init file.

When computing the lispdir emacs was previously invoked with the '-q'
option to avoid loading the users initialisation files, however, the
site wide initialisation file was still loaded, in some cases this can
cause emacs to hang, with the result that a configure can also hang.

The lisp code that aclocal causes to be executed reduces the load-path
list (in emacs) to empty.  The load-path is used by emacs to find
packages which it wants to load.  Currently, if emacs tries to auto
load a package during shut down, and the package is not found, then
emacs will hang.  This does seem like an emacs bug, but protecting
against this in aclocal is simply a case of not loading the site wide
initialisation file.

In this patch then the '-q' option to emacs is replaced with '-Q',
this has the same, the '-Q' option is similar to '-q --no-site-file
--no-splash'.

* doc/automake.texi (Hard-Coded Install Paths): Update explanation of
emacs code used to get lispdir.
* m4/lispdir.m4 (AM_PATH_LISPDIR): Update emacs flags.

Copyright-paperwork-exempt: yes
Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>