[llvm] [llvm] Set emulated-tls by default for x86_64-windows-gnu target (PR #79542)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

And another practical concern: This breaks at least one test in the testsuite, `CodeGen/X86/tls.ll`, as shown in the CI tests here. Possibly more, if running the full LLVM+Clang tests in a native mingw environment - these would need to be checked and updated accordingly.

https://github.com/llvm/llvm-project/pull/79542