With autoconf, hashtable support is built along with Xres support.

Yet, glvnd also use it, so when disabling Xres from configure, the
build will fail at link time because hashtable functions are not
available.

Untie the build of hashtable from Xres support, just like meson build
does.
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Closes: xorg/xserver#1091
(cherry picked from commit 899cebb7)