Asan: Remove initializer for tsd_key

This caused a crash in asan with the current state of constructors and destructors. Originally, it's meant to be a thread_local with a constructor that runs lazily on first use. Currently in cheerp, thread_local constructors are not supported. Removing the initializer is safe because the struct is only ever used as a global, and it's initialized to zero by default.
This was not a problem before, because the constructor was never run. Since it initialized to zero it had no effect. With the work on global destructors however, there is now a reason to run this constructor.

Author: Maqrkk

compiler-rt/lib/asan/asan_cheerpwasm.cpp

@@ -39,8 +39,11 @@ void FlushUnneededASanShadowMemory(uptr p, uptr size) {}
 
 static void (*tsd_destructor)(void *tsd) = nullptr;
 
+// Cheerp: for now we've removed the initializer for tsd_key's constructor.
+//   It caused a crash in ASAN because the constructor for the global is run after the asan module constructor has already used and set it.
+//   Originally the global is meant to be a thread_local, but thread_local constructors and destructors are not yet supported.
 struct tsd_key {
-  tsd_key() : key(nullptr) {}
+  tsd_key() {}
   ~tsd_key() {
     CHECK(tsd_destructor);
     if (key)