build: Temporarily add -Wno-error-bool-operation

ToT Clang now warns on some code in Courgette, causing the ToT bots to
fail because of -Werror. This change temporarily downgrades bool-operation
to a warning so we can continue to build while we work on a fix.

Bug: 1011810
Change-Id: I97d248539a0a3427fc374a7f4525e96234ef801e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1846084Reviewed-by: Reid Kleckner <rnk@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703551}

build/config/compiler/BUILD.gn

@@ -1538,6 +1538,13 @@ config("default_warnings") {
           # TODO(https://crbug.com/995993): Clean up and enable.
           "-Wno-implicit-fallthrough",
         ]
+
+        if (llvm_force_head_revision) {
+          cflags += [
+            # TODO(https://crbug.com/1011810): Re-enable once fix is in.
+            "-Wno-error=bool-operation",
+          ]
+        }
       }
     }
   }