Move call to initialize_collection back to initialization

Foreign thread adoption can cause additional calls to
`jl_init_thread_heap()` with a `ptls` that has `tid` 0. Thus we cannot
use that condition to ensure that `initialize_collection` is called only
once. Move the call back to `init.c`.

Author: kpamnany

src/init.c

@@ -806,6 +806,9 @@ JL_DLLEXPORT void julia_init(JL_IMAGE_SEARCH rel)
 
     jl_ptls_t ptls = jl_init_threadtls(0);
 
+#ifdef MMTK_GC
+    initialize_collection((void *)ptls);
+#endif
 #pragma GCC diagnostic push
 #if defined(_COMPILER_GCC_) && __GNUC__ >= 12
 #pragma GCC diagnostic ignored "-Wdangling-pointer"

src/mmtk-gc.c

@@ -266,9 +266,6 @@ void jl_init_thread_heap(jl_ptls_t ptls)
 
     MMTk_Mutator mmtk_mutator = bind_mutator((void *)ptls, ptls->tid);
     ptls->mmtk_mutator_ptr = ((MMTkMutatorContext*)mmtk_mutator);
-
-    if (ptls->tid == 0)
-        initialize_collection((void *)ptls);
 }
 
 // System-wide initialization