Meta issue for ucrt support

[Keno]

This issue tracks all the various pieces that are required to close #44006 and ship ucrt binaries of julia. It is intended to be a dynamic list that things get added to as new issues are discovered.

Fixes required for building a local ucrt build

• Add ucrt abi tags to binaryplatforms (Add ABI tags for windows libc, c++ stdlib flavor #59009 WIP/RFC: Add abi tags for ucrt/cxxlib #59029)
• [Driver][MinGW] Always put libc argument last, even if non-standard llvm/llvm-project#149434
• lib/Makefile: fix MinGW installation issues facebook/zstd#4441
• bump libblastrampoline
• build: More msys2 fixes #59028

Ecosystem readiness

• Add ucrt mingw toolchain to yggdrasil (Depends on 0_RootFS: Update MinGW sources JuliaPackaging/Yggdrasil#11664)
• Create a BinaryBuilder auditor pass that rejects msvcrt.dll imports
• [clang][MinGW] Implement -mcrtdll option to switch crt choice llvm/llvm-project#149469
• 7zip doesn't build - either fix or (remove replace 7z with gzip Pkg.jl#3824)
• Decide how to handle the ABI difference in CSL

[Keno]

All right, good news, I was able to build a full end-to-end ucrt julia build and didn't encounter any major build issues, so I think the major work item is just to get the few fixes in and then configure Yggdrasil (which should also not be too bad)

[Keno]

# ./usr/bin/julia.exe
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.13.0-DEV.877 (2025-07-17)
 _/ |\__'_|_|_|\__'_|  |  kf/platformupgrades/e96c8d1cac* (fork: 1 commits, 0 days)
|__/                   |

julia> Base.BinaryPlatforms.host_triplet()
"x86_64-w64-ucrt-mingw32-libgfortran5-cxx11-julia_version+1.13.0"

[ViralBShah]

I believe this should also help excise openlibm: #56875

[nhz2]

Does JuliaPackaging/Yggdrasil#12372 help with this?