assert(is_aligned(class_space_rs.base(), class_space_alignment)) failed: Sanity

The following assert was observed in our CI/CD which can be reproduced by runtime/cds/appcds/SharedBaseAddress.java and runtime/cds/SharedBaseAddress.java
---------------------------------------------------------
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/data/workspace/jdk15/src/hotspot/share/memory/metaspaceShared.cpp:2543), pid=27502, tid=27505
# assert(is_aligned(class_space_rs.base(), class_space_alignment)) failed: Sanity
#
# JRE version: (15.0) (fastdebug build )
# Java VM: OpenJDK 64-Bit Server VM (fastdebug 15-internal+0-adhoc.root.jdk15, mixed mode, sharing, tiered, compressed oops, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x118ad04] MetaspaceShared::reserve_address_space_for_archives(FileMapInfo*, FileMapInfo*, bool, ReservedSpace&, ReservedSpace&)+0x564
---------------------------------------------------------


```
Stack: [0x00007fea99408000,0x00007fea99509000], sp=0x00007fea99507750, free space=1021k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x118ad04] MetaspaceShared::reserve_address_space_for_archives(FileMapInfo*, FileMapInfo*, bool, ReservedSpace&, ReservedSpace&)+0x564
V [libjvm.so+0x118d86f] MetaspaceShared::map_archives(FileMapInfo*, FileMapInfo*, bool)+0xcf
V [libjvm.so+0x118de53] MetaspaceShared::initialize_runtime_shared_and_meta_spaces()+0xc3
V [libjvm.so+0x11842fd] Metaspace::global_initialize()+0x42d
V [libjvm.so+0x16bf6fa] universe_init()+0xca
V [libjvm.so+0xc1ccce] init_globals()+0x5e
V [libjvm.so+0x167ddc7] Threads::create_vm(JavaVMInitArgs*, bool*)+0x287
V [libjvm.so+0xd9a7a9] JNI_CreateJavaVM+0x99
C [libjli.so+0x415a] JavaMain+0x8a
C [libjli.so+0x7a39] ThreadJavaMain+0x9
```

It might be fixed by:
```
diff -r 1c81917f228b src/hotspot/share/memory/metaspaceShared.cpp
--- a/src/hotspot/share/memory/metaspaceShared.cpp Fri Jun 12 14:33:20 2020 -0700
+++ b/src/hotspot/share/memory/metaspaceShared.cpp Sat Jun 13 16:51:46 2020 +0800
@@ -2502,8 +2502,8 @@
          "CompressedClassSpaceSize malformed: "
          SIZE_FORMAT, CompressedClassSpaceSize);

- const size_t ccs_begin_offset = align_up(archive_space_size,
- class_space_alignment);
+ const size_t ccs_begin_offset = align_up((size_t)base_address + archive_space_size,
+ class_space_alignment) - (size_t)base_address;
   const size_t gap_size = ccs_begin_offset - archive_space_size;

   const size_t total_range_size =
```