Xcode 4.5.1 Release was released on 3 Oct 2012 and requires macOS 10.7+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/xcode_4.5.1/xcode4510417539a.dmg.
Release notes are located at https://download.developer.apple.com/Developer_Tools/xcode_4.5.1/release_notes_xcode_4.5.1.pdf.
The SDKs it contains are:
- iOS 10A403
- macOS 11E52
- macOS 12C237
The compilers it contains are:
- clang 4.1 (Build 421.11.66)
- LLVM-GCC (Build 2336.11.00)