Implement BasicMacroExpansionContext.buildConfiguration#3191

jmschonfeld wants to merge 2 commits intoswiftlang:mainswiftlang/swift-syntax:mainfrom

jmschonfeld:basicmacroexpansioncontext-buildconfigjmschonfeld/swift-syntax:basicmacroexpansioncontext-buildconfigCopy head branch name to clipboard