[build-script] Add optional options for header/lib paths to the syntax parser library
[build-script] Add optional options for header/lib paths to the syntax parser library

When using swift from an installed toolchain the syntax parser library will be in swift's default
search paths, but during a build-script build swift-syntax is built without having an installed toolchain available.

This could be reverted once we have a model where build-script creates a complete toolchain before building swift-syntax.

apple/swift-syntax,apple/swift-syntax,apple/swift-syntax