Suppress _emscripten_builtin_pthread_create as leaky

Author: kleisauke

system/lib/compiler-rt/lib/lsan/lsan_common.cpp

@@ -108,6 +108,13 @@ static const char kStdSuppressions[] =
 #if SANITIZER_MAC
     // For Darwin and os_log/os_trace: https://reviews.llvm.org/D35173
     "leak:*_os_trace*\n"
+#endif
+#if SANITIZER_EMSCRIPTEN
+    // On Emscripten, LSan checks for leaks during atexit(), which is called before all threads are
+    // terminated. Since LockStuffAndStopTheWorld() calls the callback on the main thread, instead
+    // of running the callback on the list of suspended threads, LSan is considering allocations
+    // within pthread_create as leaky. This supression was added to avoid that.
+    "leak:_emscripten_builtin_pthread_create\n"
 #endif
     // TLS leak in some glibc versions, described in
     // https://sourceware.org/bugzilla/show_bug.cgi?id=12650.