[cmake] Bump minimum version to 3.4.3

[modocache]

This pull request depends on #5112, which fixes warnings that are upgraded to errors in CMake 3.4.3. Please review that pull request before this one.

The Swift README states that the minimum CMake version required to build the Swift project is the same as LLVM's: 3.4.3. Bump the minimum version used by CMake to correspond to the README.

This addresses a suggestion left by @gottesmm and @llvm-beanz on #4999.

[rintaro]

When I tried this once, IIRC, swift-remoteast-test target need ENABLE_EXPORTS to compile because of CMP0065:

set_target_properties(swift-remoteast-test PROPERTIES ENABLE_EXPORTS 1)

[modocache]

Oh cool, thanks for the tip!

When I tried this once

Do you still have that code somewhere? I'd be happy to resurrect your pull request, as opposed to using this one. :)

[rintaro]

Can't we remove all these cmake_policy definition?

https://cmake.org/cmake/help/v3.4/manual/cmake-policies.7.html

The cmake_minimum_required() command does more than report an error if a too-old version of CMake is used to build a project. It also sets all policies introduced in that CMake version or earlier to NEW behavior.

[modocache]

Oh, cool! Done! Thanks!

[llvm-beanz]

The LLVM_COMMON_DEPENDS part of this patch is actually hacking around a bug in LLVM's handling of LLVM_ENABLE_MODULES I would rather we didn't do that in Swift and instead fixed the bug in LLVM.

What is happening in LLVM is that when you set LLVM_ENABLE_MODULES=On intrinsics_gen gets added as a target of basically everything. That is done so that everything ends up depending on module generation. That is a hack. The bug you're seeing is that by putting intrinsics_gen in LLVM_COMMON_DEPENDS at the root CMakeLists file in LLVM it ends up getting written into the LLVMConfig.cmake export file. LLVM should never put anything in LLVM_COMMON_DEPENDS in the export file unless it is a target being exported. Since intrinsics_gen doesn't install any files, it doesn't exist in the exported targets.

I spoke with @vedantk about this last week. I'll circle back with him this morning, and we can get a fix into LLVM trunk and into swift-llvm this morning.

[rintaro]

Code is here master...rintaro:cmake-3.4.3, that's all I modified :)
I don't have PR for this because I haven't tested this in macOS environment.

[modocache]

@swift-ci please clean test

[swift-ci]

Build failed
Jenkins build - Swift Test Linux Platform
Git Commit - 6eab4159d5a2ec3a331d449d21bdb533c543c7ea
Test requested by - @modocache

[modocache]

@swift-ci please clean test

[modocache]

The builds passed! Can I get someone's stamp of approval on this, to bring our CMake into 3.4.3? 😍

Also, thanks to @rintaro -- this pull request is nearly exactly what he wrote in master...rintaro:cmake-3.4.3. 🙇

[modocache]

Whee! Thanks, @gottesmm!