[build] Add MB and CQ configs for new gcc debug bots

Keeping the CQ bot experimental for now. Will be converted to a regular bot in a follow up.

NOTRY=true
NOTREECHECKS=true
Bug: v8:6355

Change-Id: I094cc26c8fd89bc6fda761d6bfd848a5e3b6dcb5
Reviewed-on: https://chromium-review.googlesource.com/496186
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45100}

infra/config/cq.cfg

@@ -46,6 +46,10 @@ verifiers {
         name: "v8_linux64_avx2_rel_ng_triggered"
         triggered_by: "v8_linux64_avx2_rel_ng"
       }
+      builders {
+        name: "v8_linux64_gcc_compile_dbg"
+        experiment_percentage: 100
+      }
       builders { name: "v8_linux64_gyp_rel_ng" }
       builders {
         name: "v8_linux64_gyp_rel_ng_triggered"

infra/mb/mb_config.pyl

@@ -98,6 +98,7 @@
           'gn_debug_simulate_mipsel_asan_edge',
       # Misc.
       'V8 Linux gcc 4.8': 'gn_release_x86_gcc',
+      'V8 Linux64 gcc 4.8 - debug': 'gn_debug_x64_gcc',
       # FYI.
       'V8 Linux - swarming staging': 'gn_release_x64',
       # TODO(machenbach): Figure out if symbolized is still needed. The
@@ -177,6 +178,7 @@
       'v8_linux_nosnap_dbg': 'gn_debug_x86_no_snap_trybot',
       'v8_linux_gcc_compile_rel': 'gn_release_x86_gcc_minimal_symbols',
       'v8_linux_gcc_rel': 'gn_release_x86_gcc_minimal_symbols',
+      'v8_linux64_gcc_compile_dbg': 'gn_debug_x64_gcc',
       'v8_linux64_rel_ng': 'gn_release_x64_valgrind_trybot',
       'v8_linux64_verify_csa_rel_ng': 'gn_release_x64_verify_csa',
       'v8_linux64_gyp_rel_ng': 'gyp_release_x64',
@@ -378,6 +380,8 @@
       'gn', 'debug_bot', 'x64', 'asan', 'lsan', 'edge'],
     'gn_debug_x64_custom': [
       'gn', 'debug_bot', 'x64', 'swarming', 'v8_snapshot_custom'],
+    'gn_debug_x64_gcc': [
+      'gn', 'debug_bot', 'x64', 'gcc'],
     'gn_debug_x64_minimal_symbols': [
       'gn', 'debug_bot', 'x64', 'minimal_symbols', 'swarming'],
     'gn_debug_x64_trybot': [