Suppress -Wnonportable-include-path on clang tot bots

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 785cdf3f5bc179e8d83b726d10f82074708f9d7f..6f462beabc05be2d25c5951ab34e2bf69624fc90 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1005,6 +1005,13 @@ config("default_warnings") {
         # TODO(thakis): https://crbug.com/604888
         "-Wno-undefined-var-template",
       ]
+
+      if (llvm_force_head_revision) {
+        cflags += [
+          # TODO(thakis): https://crbug.com/617318
+          "-Wno-nonportable-include-path",
+        ]
+      }
     }
   }
 }