Merge libitm changes to configure.ac from gcc master.

configure

@@ -2681,6 +2681,7 @@ target_libraries="target-libgcc \
 		target-libgloss \
 		target-newlib \
 		target-libgomp \
+		target-libitm \
 		target-libstdc++-v3 \
 		target-libmudflap \
 		target-libssp \
@@ -3056,6 +3057,25 @@ if test x$enable_libgomp = x ; then
     esac
 fi
 
+# Disable libitm on unsupported systems.
+if test -d ${srcdir}/libitm; then
+    if test x$enable_libitm = x; then
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for libitm support" >&5
+$as_echo_n "checking for libitm support... " >&6; }
+	if (srcdir=${srcdir}/libitm; \
+		. ${srcdir}/configure.tgt; \
+		test -n "$UNSUPPORTED")
+	then
+	    { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+	    noconfigdirs="$noconfigdirs target-libitm"
+	else
+	    { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+	fi
+    fi
+fi
+
 # Disable libssp for some systems.
 case "${target}" in
   avr-*-*)