swift234

built-script: Add --swift-stdlib-sil-serialize-all flag

We want to have the option of building the standard library without
-sil-serialize-all.

For now, the build crashes in the SIL verifier due to various issues;
upcoming patches will address these.

This is part of the larger goal of building the stdlib with
-enable-resilience.

Part of https://bugs.swift.org/browse/SR-267.