openjdk: 14.0.2 -> 15.0.1

* update two explicit references to jdk14 to just jdk, which no longer
  points at jdk8 after #89731.

* patch an explicit -XX:+UseConcMarkSweepGC to -XX:UseG1GC, as the
  former now throws an error (after having been deprecated since jdk 9)

pkgs/servers/jitsi-videobridge/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, dpkg, jre_headless, nixosTests }:
+{ stdenv, fetchurl, makeWrapper, dpkg, jre_headless, nixosTests }:
 
 let
   pname = "jitsi-videobridge2";
@@ -15,6 +15,8 @@ stdenv.mkDerivation {
 
   unpackCmd = "${dpkg}/bin/dpkg-deb -x $src debcontents";
 
+  buildInputs = [ makeWrapper ];
+
   installPhase = ''
     substituteInPlace usr/share/jitsi-videobridge/jvb.sh \
       --replace "exec java" "exec ${jre_headless}/bin/java"
@@ -24,6 +26,10 @@ stdenv.mkDerivation {
     cp ${./logging.properties-journal} $out/etc/jitsi/videobridge/logging.properties-journal
     mv usr/share/jitsi-videobridge/* $out/share/jitsi-videobridge/
     ln -s $out/share/jitsi-videobridge/jvb.sh $out/bin/jitsi-videobridge
+
+    # work around https://github.com/jitsi/jitsi-videobridge/issues/1547
+    wrapProgram $out/bin/jitsi-videobridge \
+      --set VIDEOBRIDGE_GC_TYPE G1GC
   '';
 
   passthru.tests = {