[11] RFR: Cease support for shenandoah/jdk11

[Aleksey Shipilev]

I think it is time to sunset the sh/jdk11 repository, like we did for sh/jdk12:
  https://hg.openjdk.java.net/shenandoah/jdk12/rev/4436df5d798c

sh/jdk11 only difference against jdk11 upstream are tags and enabling Shenandoah during build:
  https://builds.shipilev.net/patch-openjdk-shenandoah-jdk11/

Let's add this patch to sh/jdk11:

diff -r 4f528121104a src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp
--- a/src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp   Wed Aug 12 09:19:23 2020 +0200
+++ b/src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp   Wed Aug 12 09:42:36 2020 +0200
@@ -29,10 +29,19 @@
 #include "utilities/defaultStream.hpp"

 void ShenandoahArguments::initialize() {
+  log_warning(gc)("**************************************************************************");
+  log_warning(gc)("*  Shenandoah/JDK 11 is now maintained in upstream OpenJDK 11.           *");
+  log_warning(gc)("*  This JDK would not get security, functionality or performance fixes.  *");
+  log_warning(gc)("*  Use this build at your own risk.                                      *");
+  log_warning(gc)("*                                                                        *");
+  log_warning(gc)("*  For the latest version, use the most recent OpenJDK 11 update release *");
+  log_warning(gc)("*  from the vendor that has Shenandoah enabled in their builds.          *");
+  log_warning(gc)("**************************************************************************");
+
 #if !(defined AARCH64 || defined AMD64 || defined IA32)
   vm_exit_during_initialization("Shenandoah GC is not supported on this platform.");
 #endif

Testing: sh/jdk11 builds, observing the warning message

-- 
Thanks,
-Aleksey