iOS: Fix detection of supported SDK architectures
Instead of relying on SDKSettings.plist which does not contain the certain architectures, deduce the supported architectures by inspecting libSystem.tbd and libSystem.dylib.
.tbd files are text files, so just parse out the archs string. .dylib files can be fat or non-fat, so use lipo -info to extract the architectures and parse lipo output.
Fixes: #20588 (closed)