Xcode 7.3 Release was released on 21 Mar 2016 and requires macOS 10.11+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/Xcode_7.3/Xcode_7.3.dmg.
Release notes are located at https://developer.apple.com/library/content/releasenotes/DeveloperTools/RN-Xcode/Chapters/Introduction.html#//apple_ref/doc/uid/TP40001051-CH1-SW233.
The SDKs it contains are:
- iOS 13E230
- macOS 15E60
- tvOS 13Y227
- watchOS 13V143
The compilers it contains are:
- clang 7.3.0 (Build 703.0.29)
- swift 2.2 (Build 703.0.18.1)
- LLVM-GCC 3.8.0 (Build )