Clang ignores -femulated-tls on Darwin with LTO enabled

[Un1q32]

tls.c:

#include <pthread.h>
#include <stdio.h>

__thread int var = 0;

void *func(void *arg) {
  (void)arg;
  if (var == 0)
    var = 1;
  else
    puts("race");
  return NULL;
}

int main(void) {
  pthread_t ptid;
  int i = 0;
  while (i < 10) {
    pthread_create(&ptid, NULL, func, NULL);
    i++;
  }
  return 0;
}

Run on macOS:

$ clang -mmacos-version-min=14.0 tls.c -c
$ ld -arch x86_64 -platform_version macos 14.0 14.0 tls.o
Undefined symbols for architecture x86_64:
  "__tlv_bootstrap", referenced from:
      _var in tls.o
  "_pthread_create", referenced from:
      _main in tls.o
  "_puts", referenced from:
      _func in tls.o
ld: symbol(s) not found for architecture x86_64
$ # __tlv_bootstrap indicates normal TLS
$ clang -mmacos-version-min=14.0 tls.c -c -femulated-tls
$ ld -arch x86_64 -platform_version macos 14.0 14.0 tls.o
Undefined symbols for architecture x86_64:
  "___emutls_get_address", referenced from:
      _func in tls.o
      _func in tls.o
  "_pthread_create", referenced from:
      _main in tls.o
  "_puts", referenced from:
      _func in tls.o
ld: symbol(s) not found for architecture x86_64
$ # ___emutls_get_address indicates emulated TLS
$ clang tls.c -c -femulated-tls -flto
$ ld -arch x86_64 -platform_version macos 14.0 14.0 tls.o
Undefined symbols for architecture x86_64:
  "__tlv_bootstrap", referenced from:
      _var in lto.o
  "_pthread_create", referenced from:
      _main in lto.o
  "_puts", referenced from:
      _func in lto.o
ld: symbol(s) not found for architecture x86_64
$ # __tlv_bootstrap is used dispite -femulated-tls being passed.

It happens when using -emit-llvm instead of -flto too. My guess is that the TLS model used is decided after LLVM IR generation, is there a workaround to use emulated TLS with LTO?

[Un1q32]

Closing because I now understand this would be impossible to fix without making a change in Apple's linker.