configure: add --disable-tcg configure option

This lets you build without TCG (hardware accelerationor qtest only).  When
this flag is passed to configure, it will automatically filter out the target
list to only those that support KVM or Xen or HAX.
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

configure

@@ -232,7 +232,12 @@ supported_target() {
             return 1
             ;;
     esac
-    return 0
+    test "$tcg" = "yes" && return 0
+    supported_kvm_target "$1" && return 0
+    supported_xen_target "$1" && return 0
+    supported_hax_target "$1" && return 0
+    print_error "TCG disabled, but hardware accelerator not available for '$target'"
+    return 1
 }
 
 # default parameters
@@ -296,6 +301,7 @@ cap_ng=""
 attr=""
 libattr=""
 xfs=""
+tcg="yes"
 
 vhost_net="no"
 vhost_scsi="no"
@@ -1033,6 +1039,10 @@ for opt do
   ;;
   --enable-cap-ng) cap_ng="yes"
   ;;
+  --disable-tcg) tcg="no"
+  ;;
+  --enable-tcg) tcg="yes"
+  ;;
   --disable-spice) spice="no"
   ;;
   --enable-spice) spice="yes"
@@ -5195,7 +5205,6 @@ echo "module support    $modules"
 echo "host CPU          $cpu"
 echo "host big endian   $bigendian"
 echo "target list       $target_list"
-echo "tcg debug enabled $debug_tcg"
 echo "gprof enabled     $gprof"
 echo "sparse enabled    $sparse"
 echo "strip binaries    $strip_opt"
@@ -5250,8 +5259,12 @@ echo "ATTR/XATTR support $attr"
 echo "Install blobs     $blobs"
 echo "KVM support       $kvm"
 echo "HAX support       $hax"
+echo "TCG support       $tcg"
+if test "$tcg" = "yes" ; then
+    echo "TCG debug enabled $debug_tcg"
+    echo "TCG interpreter   $tcg_interpreter"
+fi
 echo "RDMA support      $rdma"
-echo "TCG interpreter   $tcg_interpreter"
 echo "fdt support       $fdt"
 echo "preadv support    $preadv"
 echo "fdatasync         $fdatasync"
@@ -5694,8 +5707,11 @@ fi
 if test "$signalfd" = "yes" ; then
   echo "CONFIG_SIGNALFD=y" >> $config_host_mak
 fi
-if test "$tcg_interpreter" = "yes" ; then
-  echo "CONFIG_TCG_INTERPRETER=y" >> $config_host_mak
+if test "$tcg" = "yes"; then
+  echo "CONFIG_TCG=y" >> $config_host_mak
+  if test "$tcg_interpreter" = "yes" ; then
+    echo "CONFIG_TCG_INTERPRETER=y" >> $config_host_mak
+  fi
 fi
 if test "$fdatasync" = "yes" ; then
   echo "CONFIG_FDATASYNC=y" >> $config_host_mak