build: Fix Inspector package build with Xcode 11

Cherry-pick commits from original WebKit fixing errors reported by Xcode 11's build toolchain.

PR Checklist

[x] The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
[ ] There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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[x] All existing tests are passing: https://github.com/NativeScript/ios-runtime/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
[ ] Tests for the changes are included.