Add a configure switch to enable / disable all user targets. I felt compelled to do it for symmetry, mostly it is useful to disable user targets when you don't want to build them.

Signed-off-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/configure b/configure
index 0b2c721..38503b2 100755
--- a/configure
+++ b/configure
@@ -471,6 +471,12 @@
   ;;
   --enable-system) softmmu="yes"
   ;;
+  --disable-user)
+      linux_user="no" ;
+      bsd_user="no" ;
+      darwin_user="no"
+  ;;
+  --enable-user) ;;
   --disable-linux-user) linux_user="no"
   ;;
   --enable-linux-user) linux_user="yes"
@@ -629,6 +635,8 @@
 echo "  --disable-nptl           disable usermode NPTL support"
 echo "  --enable-system          enable all system emulation targets"
 echo "  --disable-system         disable all system emulation targets"
+echo "  --enable-user            enable supported user emulation targets"
+echo "  --disable-user           disable all user emulation targets"
 echo "  --enable-linux-user      enable all linux usermode emulation targets"
 echo "  --disable-linux-user     disable all linux usermode emulation targets"
 echo "  --enable-darwin-user     enable all darwin usermode emulation targets"