Avoid Valgrind message due to glibc bug. (#3768)

runtime/src/main/cpp/Porting.cpp

@@ -140,7 +140,19 @@ static void onThreadExitCallback(void* value) {
   pthread_setspecific(terminationKey, nullptr);
 }
 
+#if KONAN_LINUX
+static pthread_key_t dummyKey;
+#endif
 static void onThreadExitInit() {
+#if KONAN_LINUX
+  // Due to glibc bug we have to create first key as dummy, to avoid
+  // conflicts with potentially uninitialized dlfcn error key.
+  // https://code.woboq.org/userspace/glibc/dlfcn/dlerror.c.html#237
+  // As one may see, glibc checks value of the key even if it was not inited (and == 0),
+  // and so data associated with our legit key (== 0 as being the first one) is used.
+  // Other libc are not affected, as usually == 0 pthread key is impossible.
+  pthread_key_create(&dummyKey, nullptr);
+#endif
   pthread_key_create(&terminationKey, onThreadExitCallback);
 }