[Misc] Use CMS as default GC policy

Summary:
- Port fix D2553 to Dragonwell
- Change default GC policy to UseConcMarkSweepGC

Test Plan: hotspot/test/gc/TestDefaultGC.sh

Reviewers: 井桐

Reviewed By: 井桐

Subscribers:

Differential Revision: https://aone.alibaba-inc.com/code/D849276

src/share/vm/runtime/arguments.cpp

@@ -1581,7 +1581,7 @@ void Arguments::select_gc_ergonomically() {
 
 void Arguments::select_gc() {
   if (!gc_selected()) {
-    select_gc_ergonomically();
+    FLAG_SET_ERGO(bool, UseConcMarkSweepGC, true);
   }
 }
 

test/gc/TestDefaultGC.sh

@@ -0,0 +1,38 @@
+#
+# Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+# DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+#
+# This code is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License version 2 only, as
+# published by the Free Software Foundation. Alibaba designates this
+# particular file as subject to the "Classpath" exception as provided
+# by Oracle in the LICENSE file that accompanied this code.
+#
+# This code is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+# version 2 for more details (a copy is included in the LICENSE file that
+# accompanied this code).
+#
+# You should have received a copy of the GNU General Public License version
+# 2 along with this work; if not, write to the Free Software Foundation,
+# Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+#
+
+#
+# @test
+# @summary test the default gc
+# @run shell TestDefaultGC.sh
+#
+
+${TESTJAVA}/bin/java -XX:+PrintFlagsFinal -version | grep UseConcMarkSweepGC |grep true
+
+if [ "0" == $? ];
+then
+    echo "CMS is Default GC"
+    echo "--- Test passed"
+else
+    echo "CMS is not Default GC"
+    echo "--- Test failed"
+    exit 1
+fi