configure: bump spice-server required version to 0.12.5

configure: bump spice-server required version to 0.12.5

Looking at chardev/spice.c code, I realize compilation was broken for
a while with spice-server < 0.12.3. Let's bump required version
to 0.12.5, released May 19 2014, instead of adding more #ifdef.

(this patch combines changes from an early version and some of
Frediano "[PATCH 2/2] spice: Bump required spice-server version to
0.12.6")

According to repology, all the distros that are build target platforms
for QEMU include it:

      RHEL-7: 0.14.0
      Debian (Stretch): 0.12.8
      Debian (Jessie): 0.12.5
      FreeBSD (ports): 0.14.0
      OpenSUSE Leap 15: 0.14.0
      Ubuntu (Xenial): 0.12.6

Note that a previous version of this patch was bumping version to
0.12.6. Unfortunately, Debian Jessie (oldstable) is stuck with spice
server 0.12.5, and QEMU should keep building until after 2y of current
stable (Stretch), which will be around June 17th 2019. Qemu 4.1
should thus be free of bumping to spice-server 0.12.6 during 4.1
development cycle.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20181128155932.16171-1-marcandre.lureau@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>