Xcode 4.2 Release was released on 12 Oct 2011 and requires macOS 10.6.8+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/xcode_4.2_for_snow_leopard/xcode_4.2_for_snow_leopard.dmg.
Release notes are located at https://download.developer.apple.com/Developer_Tools/xcode_4.2_for_snow_leopard/xcode_4.2_for_snow_leopard_readme.pdf.
The SDKs it contains are:
- iOS 9A334
The compilers it contains are:
- clang 3.0 (Build 211.10.1)
- LLVM-GCC (Build 2336.1.00)