[11] Revert upstream difference with UseShenandoahGC undefined

[Aleksey Shipilev]

Seems like non-Shenandoah sh/jdk11 builds fail with:

/home/buildbot/worker/build-shenandoah-jdk11-linux/build/src/hotspot/share/gc/shared/gcConfig.cpp:
In static member function ‘static void GCConfig::fail_if_unsupported_gc_is_selected()’:
/home/buildbot/worker/build-shenandoah-jdk11-linux/build/src/hotspot/share/gc/shared/gcConfig.cpp:105:37:
error: ‘UseShenandoahGC’ was not declared in this scope
   NOT_SHENANDOAHGC(FAIL_IF_SELECTED(UseShenandoahGC,  true));

I think we need to remove the upstream difference in gcConfig and TestDisableDefaultGC.java:
  https://builds.shipilev.net/patch-openjdk-shenandoah-jdk11/

This does it:

diff -r f01915212b47 src/hotspot/share/gc/shared/gcConfig.cpp
--- a/src/hotspot/share/gc/shared/gcConfig.cpp  Wed Aug 05 10:55:41 2020 +0200
+++ b/src/hotspot/share/gc/shared/gcConfig.cpp  Wed Aug 05 14:33:32 2020 +0200
@@ -103,5 +103,4 @@
   NOT_SERIALGC(  FAIL_IF_SELECTED(UseSerialGC,        true));
   NOT_SERIALGC(  FAIL_IF_SELECTED(UseParallelOldGC,   false));
-  NOT_SHENANDOAHGC(FAIL_IF_SELECTED(UseShenandoahGC,  true));
   NOT_ZGC(       FAIL_IF_SELECTED(UseZGC,             true));
 }
diff -r f01915212b47 test/hotspot/jtreg/gc/arguments/TestDisableDefaultGC.java
--- a/test/hotspot/jtreg/gc/arguments/TestDisableDefaultGC.java Wed Aug 05 10:55:41 2020 +0200
+++ b/test/hotspot/jtreg/gc/arguments/TestDisableDefaultGC.java Wed Aug 05 14:33:32 2020 +0200
@@ -45,5 +45,4 @@
                                                                   "-XX:-UseConcMarkSweepGC",
                                                                   "-XX:+UnlockExperimentalVMOptions",
-                                                                  "-XX:-UseShenandoahGC",
                                                                   "-XX:-UseZGC",
                                                                   "-version");

Testing: builds

-- 
Thanks,
-Aleksey