Xcode 4.3.1 Release was released on 5 Mar 2012 and requires macOS 10.7+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/xcode_4.3.1_for_lion_21267/xcode_431_lion.dmg.
The SDKs it contains are:
- iOS 9B176
The compilers it contains are:
- clang 3.1 (Build 318.0.54)
- LLVM-GCC (Build 2336.9.00)