Xcode and Qt Creator project changes needed for Andy's SIMD work

[bhaller]

In both of these environments, the new SIMD stuff is presently disabled because the configuration/enabling of it happens in the CMake configuration, which Xcode and Qt Creator don't use. @andrewkern says that we can add “OTHER_CFLAGS[arch=x86_64]” = “-mavx2 -mfma”; in the projects for these environments to enable it.

Builds in these environments also presently fail because eidos_simd.h is not added to the project, and so the includes of it fail. Once the right SIMD flags are set, builds would also fail because the sleef subfolder and files within are not added to the projects either.

Fixing all this would require changes to the project files, and I don't want to get into that right now while multitrait is so divergent and merges of project files don't work well; so for now I'm making an issue and we'll do it later. For now I think it is OK that Xcode and Qt Creator builds fail for the master branch; those environments are not really supported for end users, CMake is the supported build method. It will inconvenience me, but probably nobody else. We'll see whether anybody complains. :->

[bhaller]

@andrewkern noted that those -mavx2 -mfma flags assume AVX2 is present for x86_64, which has been true since 2013. So we'd be abandoning some very old machines; installer builds would assume SIMD, and would crash on older hardware. I think that's probably OK; 2013 is a long time ago now. If people want to run SLiM on older machines than that, they just wouldn't be able to use the installer build, they'd have to build themselves on their target hardware so the correct SIMD settings got auto-detected by CMake. For Apple Silicon this is a non-issue, because the NEON architecture for SIMD there has been present since day one.

[andrewkern]

A note for the future:

a potential way to go here is to use a .xconfig file which is a plain text file that can be selected for a particular target build within Xcode: https://developer.apple.com/documentation/xcode/adding-a-build-configuration-file-to-your-project

This would enable github maintainable build target information where e.g., a SLiM_SIMD.xconfig would contain info like

  // SIMD flags for x86_64 builds
  // ARM64 NEON is auto-detected, no flags needed
  OTHER_CFLAGS[arch=x86_64] = -mavx2 -mfma
  OTHER_CPLUSPLUSFLAGS[arch=x86_64] = $(OTHER_CFLAGS)  -mavx2 -mfma

NOTE: this still would require a change in the project.pbxproj to reference the xconfig file, but it's a much smaller change than embedding the flags directly

[bhaller]

I realized that there's a middle ground available. I added eidos_simd.h to the projects in master so they now build without errors (but do not utilize SIMD). Then I dealt with the merge into multitrait, which was straightforward since there all the other proposed changes discussed above were pended. The rest will be dealt with later, since it is less urgent. Now I can make other changes to master as needed and merge in to multitrait, which is necessary from time to time.