[5.6][build] Clean up ICU detritus that is no longer used to build the stdlib#40817

Merged

compnerd merged 3 commits intoswiftlang:release/5.6from

finagolfin:56-icu

Jan 13, 2022

Commits on Jan 12, 2022

[android] Remove ICU build flags since that requirement was dropped in #40340
finagolfin
committed
[build] Remove last vestiges of ICU for anything other than Foundation
finagolfin
committed
[build] Remove SWIFT_SDK_${OS}_ARCH_${ARCH}_LIBC_ARCHITECTURE_INCLUDE_DIRECTORY CMake variable
finagolfin
committed