[build] Disable spurious msvc warnings

TBR=yangguo@chromium.org

Bug: v8:7771
Change-Id: I81f1bdf2b4fffceef9cc4cb3ad9f3713a873e38e
Reviewed-on: https://chromium-review.googlesource.com/1065874Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53248}

BUILD.gn

@@ -581,6 +581,8 @@ config("toolchain") {
       "/wd4715",  # Not all control paths return a value.
 
       "/wd4718",  # Recursive call has no side-effect.
+      "/wd4723",  # https://crbug.com/v8/7771
+      "/wd4724",  # https://crbug.com/v8/7771
       "/wd4800",  # Forcing value to bool.
     ]
   }