[compiler-rt] [sanitizer] Fix asserts in asan and tsan in pthread interceptors. (PR #75394)

[Vitaly Buka via llvm-commits]

================
@@ -53,16 +56,30 @@ void ThreadArgRetval::Finish(uptr thread, void* retval) {
 u32 ThreadArgRetval::BeforeJoin(uptr thread) const {
   __sanitizer::Lock lock(&mtx_);
   auto t = data_.find(thread);
-  CHECK(t);
-  CHECK(!t->second.detached);
-  return t->second.gen;
+  bool detect_invalid_join = common_flags()->detect_invalid_join;
----------------
vitalybuka wrote:

```
  if (t && !t->second.detached) {
    return t->second.gen;
  }
  if (!common_flags()->detect_invalid_join)
     return kInvalidGen;
  const char* const reason = "unknown";
  if (!t) {
    reason = "already joined";
  } else if (t->second.detached) {
    reason = "detached";
  } 
  Report("ERROR: %s: Joining %s thread, aborting.\n",
               SanitizerToolName, reason);
  Die();
```

https://github.com/llvm/llvm-project/pull/75394