configure: add --enable-plugins

This adds the basic boilerplate feature enable option for the build.
We shall expand it later.

[AJB: split from larger patch]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

configure

@@ -498,6 +498,7 @@ libxml2=""
 debug_mutex="no"
 libpmem=""
 default_devices="yes"
+plugins="no"
 
 supported_cpu="no"
 supported_os="no"
@@ -1529,6 +1530,10 @@ for opt do
   ;;
   --disable-xkbcommon) xkbcommon=no
   ;;
+  --enable-plugins) plugins="yes"
+  ;;
+  --disable-plugins) plugins="no"
+  ;;
   *)
       echo "ERROR: unknown option $opt"
       echo "Try '$0 --help' for more information"
@@ -1710,6 +1715,8 @@ Advanced options (experts only):
   --enable-profiler        profiler support
   --enable-debug-stack-usage
                            track the maximum stack usage of stacks created by qemu_alloc_stack
+  --enable-plugins
+                           enable plugins via shared library loading
 
 Optional features, enabled with --enable-FEATURE and
 disabled with --disable-FEATURE, default is enabled if available:
@@ -6442,6 +6449,7 @@ echo "capstone          $capstone"
 echo "libpmem support   $libpmem"
 echo "libudev           $libudev"
 echo "default devices   $default_devices"
+echo "plugin support    $plugins"
 
 if test "$supported_cpu" = "no"; then
     echo
@@ -7272,6 +7280,11 @@ if test "$sheepdog" = "yes" ; then
   echo "CONFIG_SHEEPDOG=y" >> $config_host_mak
 fi
 
+if test "$plugins" = "yes" ; then
+    echo "CONFIG_PLUGIN=y" >> $config_host_mak
+    LIBS="-ldl $LIBS"
+fi
+
 if test "$tcg_interpreter" = "yes"; then
   QEMU_INCLUDES="-iquote \$(SRC_PATH)/tcg/tci $QEMU_INCLUDES"
 elif test "$ARCH" = "sparc64" ; then