java/openjdk13: fix build with clang 12

During an exp-run for llvm 12 (see bug 255570), it turned out that at
least openjdk11 and openjdk12 do not build with clang 12.0.0. The
exp-run therefore skipped openjdk13.

Building this manually shows that it results in a compile error:

gmake[4]: Leaving directory '/wrkdirs/usr/ports/java/openjdk13/work/openjdk-jdk13u-jdk-13.0.7-1-1/make'
/wrkdirs/usr/ports/java/openjdk13/work/openjdk-jdk13u-jdk-13.0.7-1-1/src/hotspot/cpu/x86/vm_version_ext_x86.cpp:748:3: error: suspicious concatenation of string literals in an array initialization; did you mean to separate the elements with a comma? [-Werror,-Wstring-concatenation]
  "",
  ^
/wrkdirs/usr/ports/java/openjdk13/work/openjdk-jdk13u-jdk-13.0.7-1-1/src/hotspot/cpu/x86/vm_version_ext_x86.cpp:747:3: note: place parentheses around the string literal to silence warning
  "Opteron QC/Phenom"  // Barcelona et.al.
  ^
1 error generated.

This is due to a missing backport of this upstream commit:

commit f8a9602a0a65cdc98eb940aac9529256ded2bf42
Author: Yasumasa Suenaga <ysuenaga@openjdk.org>
Date:	Thu Jan 21 06:08:13 2021 +0000

    8260025: Missing comma in VM_Version_Ext::_family_id_amd

    Reviewed-by: dholmes, stuefe

Even after applying this fix, there is still a possibility of a segfault
during the build, due to another missing backport, of this upstream
commit:

commit c484d8904285652246c3af212a4211b9a8955149
Author: Thomas Stuefe <stuefe@openjdk.org>
Date:	Tue Mar 16 05:49:01 2021 +0000

    8263557: Possible NULL dereference in Arena::destruct_contents()

    Reviewed-by: kbarrett, coleenp

Approved by:	maintainer timeout (2 weeks)
PR:		255902
MFH:		2021Q2

2 files changed, 51 insertions, 0 deletions

diff --git a/java/openjdk13/files/patch-commit-c484d890428 b/java/openjdk13/files/patch-commit-c484d890428
new file mode 100644
index 000000000000..39ac7a7e8e46
--- /dev/null
+++ b/java/openjdk13/files/patch-commit-c484d890428
@@ -0,0 +1,23 @@
+commit c484d8904285652246c3af212a4211b9a8955149
+Author: Thomas Stuefe <stuefe@openjdk.org>
+Date:   Tue Mar 16 05:49:01 2021 +0000
+
+    8263557: Possible NULL dereference in Arena::destruct_contents()
+    
+    Reviewed-by: kbarrett, coleenp
+
+diff --git src/hotspot/share/memory/arena.cpp src/hotspot/share/memory/arena.cpp
+index 8388f68c359..16059bed9be 100644
+--- src/hotspot/share/memory/arena.cpp
++++ src/hotspot/share/memory/arena.cpp
+@@ -310,7 +310,9 @@ void Arena::destruct_contents() {
+   // reset size before chop to avoid a rare racing condition
+   // that can have total arena memory exceed total chunk memory
+   set_size_in_bytes(0);
+-  _first->chop();
++  if (_first != NULL) {
++    _first->chop();
++  }
+   reset();
+ }
+ 
diff --git a/java/openjdk13/files/patch-commit-f8a9602a0a6 b/java/openjdk13/files/patch-commit-f8a9602a0a6
new file mode 100644
index 000000000000..3222f6ceb871
--- /dev/null
+++ b/java/openjdk13/files/patch-commit-f8a9602a0a6
@@ -0,0 +1,28 @@
+commit f8a9602a0a65cdc98eb940aac9529256ded2bf42
+Author: Yasumasa Suenaga <ysuenaga@openjdk.org>
+Date:   Thu Jan 21 06:08:13 2021 +0000
+
+    8260025: Missing comma in VM_Version_Ext::_family_id_amd
+    
+    Reviewed-by: dholmes, stuefe
+
+diff --git src/hotspot/cpu/x86/vm_version_ext_x86.cpp src/hotspot/cpu/x86/vm_version_ext_x86.cpp
+index 30d9494c654..a84b37f7977 100644
+--- src/hotspot/cpu/x86/vm_version_ext_x86.cpp
++++ src/hotspot/cpu/x86/vm_version_ext_x86.cpp
+@@ -1,5 +1,5 @@
+ /*
+- * Copyright (c) 2013, 2019, Oracle and/or its affiliates. All rights reserved.
++ * Copyright (c) 2013, 2021, Oracle and/or its affiliates. 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
+@@ -739,7 +739,7 @@ const char* const VM_Version_Ext::_family_id_amd[ExtendedFamilyIdLength_AMD] = {
+   "",
+   "",
+   "Opteron/Athlon64",
+-  "Opteron QC/Phenom"  // Barcelona et.al.
++  "Opteron QC/Phenom",  // Barcelona et.al.
+   "",
+   "",
+   "",