link libspice server with libm libpthread
link libspice server with libm libpthread

server/Makefile apparently forgot to link libspice-server
with -lm -lpthread, but it uses symbols from these libraries
directly.  These libs are detected by configure and stored in
$(SPICE_NONPKGCONFIG_LIBS) make variable, but this variable
is never referenced at link time.  Add it to server/Makefile.am,
to libspice_server_la_LIBADD variable.

Signed-off-By: Michael Tokarev <389bd06664b699d49ce291f515b98373073ad5f4@tls.msk.ru>

SPICE/spice,alon/spice-server,alon/spice-server,ya-mouse/spice,elmarco/spice,Fantu/spice,freedesktop-unofficial-mirror/spice__spice,fgouget/spice,fgouget/spice,alon/spice-server,alon/spice-server,Fantu/spice,fgouget/spice,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,ya-mouse/spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,Fantu/spice,fgouget/spice,ya-mouse/spice,Fantu/spice,alon/spice-server,elmarco/spice,SPICE/spice,freedesktop-unofficial-mirror/spice__spice,SPICE/spice,elmarco/spice