Eliminate --disable-gfx-check and make VNC default when SDL not available

--disable-gfx-check predates VNC server support.  It made sense back then
because the only thing you could do without SDL was use -nographic mode or
similar tricks.  Since this is a very advanced mode of operation, gfx-check
provided a good safety net for casual users.

A casual user is very likely to use VNC to interact with a guest.  In fact, it's
often frustrating to install QEMU on a server and have to specify
disable-gfx-check when you only want to use VNC.

This patch eliminates disable-gfx-check and makes SDL behave like every other
optional dependency.  If SDL is not available, instead of failing ungracefully
if no special options are specified, we default to -vnc localhost:0,to=99.
When we do default to VNC, we also print a message to tell the user that we've
done this include which port we're currently listening on.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

configure

@@ -172,7 +172,6 @@ solaris="no"
 kqemu="no"
 profiler="no"
 cocoa="no"
-check_gfx="yes"
 softmmu="yes"
 linux_user="no"
 darwin_user="no"
@@ -191,6 +190,7 @@ kerneldir=""
 aix="no"
 blobs="yes"
 fdt="yes"
+sdl="yes"
 sdl_x11="no"
 xen="yes"
 pkgversion=""
@@ -438,8 +438,6 @@ for opt do
       sdl="no" ;
       audio_drv_list="coreaudio `echo $audio_drv_list | sed s,coreaudio,,g`"
   ;;
-  --disable-gfx-check) check_gfx="no"
-  ;;
   --disable-system) softmmu="no"
   ;;
   --enable-system) softmmu="yes"
@@ -835,7 +833,7 @@ fi
 
 sdl_too_old=no
 
-if test -z "$sdl" ; then
+if test "$sdl" = "yes" ; then
     sdl_config="sdl-config"
     sdl=no
     sdl_static=no
@@ -1346,10 +1344,6 @@ echo "preadv support    $preadv"
 if test $sdl_too_old = "yes"; then
 echo "-> Your SDL version is too old - please upgrade to have SDL support"
 fi
-if [ -s $TMPSDLLOG ]; then
-  echo "The error log from compiling the libSDL test is: "
-  cat $TMPSDLLOG
-fi
 #if test "$sdl_static" = "no"; then
 #  echo "WARNING: cannot compile statically with SDL - qemu-fast won't have a graphical output"
 #fi
@@ -1772,15 +1766,6 @@ case "$target" in
     ;;
 esac
 
-if test "$target_user_only" = "no" -a "$check_gfx" = "yes" \
-        -a "$sdl" = "no" -a "$cocoa" = "no" ; then
-    echo "ERROR: QEMU requires SDL or Cocoa for graphical output"
-    echo "To build QEMU without graphical output configure with --disable-gfx-check"
-    echo "Note that this will disable all output from the virtual graphics card"
-    echo "except through VNC or curses."
-    exit 1;
-fi
-
 #echo "Creating $config_mak, $config_h and $target_dir/Makefile"
 
 test -f $config_h && mv $config_h ${config_h}~