Add two V8 Linux64 - builder shadows.

- goma cache silo is a builder to build the same target with cache silo.
  This is needed for fair build performance comparison between reclient
  and Goma.
- reclient compare is a builder to verify artifacts generated in remote
  and that generated locally matches.

Bug: chromium:1233780
Change-Id: I5854d20880e972a07fa09cfc5d4a6f9385844fbb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3058059Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Commit-Queue: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75979}

infra/mb/mb_config.pyl

@@ -62,7 +62,9 @@
       'V8 Linux - verify csa': 'release_x86_verify_csa',
       # Linux64.
       'V8 Linux64 - builder': 'release_x64',
+      'V8 Linux64 - builder (goma cache silo)': 'release_x64',
       'V8 Linux64 - builder (reclient)': 'release_x64_reclient',
+      'V8 Linux64 - builder (reclient compare)': 'release_x64_reclient',
       'V8 Linux64 - debug builder': 'debug_x64',
       'V8 Linux64 - dict tracking - debug - builder': 'debug_x64_dict_tracking_trybot',
       'V8 Linux64 - external code space - debug - builder': 'debug_x64_external_code_space',