Use correct thread stack limits in jl_init_stack_limits (#54639)

Actually these do not really seem to matter much in practice (as
explained to me by @vtjnash on Slack, thank you). The one thing that did
cause me some grief here, though, was that stack_hi was the low address
and stack_lo the high address.

A smaller change to achieve that "hi means high, lo means low" would be
to just reverse `stack_hi` and `stack_lo`.

src/init.c

@@ -71,21 +71,17 @@ void jl_init_stack_limits(int ismaster, void **stack_lo, void **stack_hi)
  size_t stacksize;
  pthread_attr_getstack(&attr, &stackaddr, &stacksize);
  pthread_attr_destroy(&attr);
- *stack_lo = (void*)stackaddr;
-#pragma GCC diagnostic push
-#if defined(_COMPILER_GCC_) && __GNUC__ >= 12
-#pragma GCC diagnostic ignored "-Wdangling-pointer"
-#endif
- *stack_hi = (void*)__builtin_frame_address(0);
-#pragma GCC diagnostic pop
+ *stack_hi = stackaddr;
+ *stack_lo = (char*)stackaddr - stacksize;
  return;
 # elif defined(_OS_DARWIN_)
  extern void *pthread_get_stackaddr_np(pthread_t thread);
  extern size_t pthread_get_stacksize_np(pthread_t thread);
  pthread_t thread = pthread_self();
  void *stackaddr = pthread_get_stackaddr_np(thread);
- *stack_lo = (void*)stackaddr;
- *stack_hi = (void*)__builtin_frame_address(0);
+ size_t stacksize = pthread_get_stacksize_np(thread);
+ *stack_hi = stackaddr;
+ *stack_lo = (char*)stackaddr - stacksize;
  return;
 # elif defined(_OS_FREEBSD_)
  pthread_attr_t attr;
@@ -95,8 +91,8 @@ void jl_init_stack_limits(int ismaster, void **stack_lo, void **stack_hi)
  size_t stacksize;
  pthread_attr_getstack(&attr, &stackaddr, &stacksize);
  pthread_attr_destroy(&attr);
- *stack_lo = (void*)stackaddr;
- *stack_hi = (void*)__builtin_frame_address(0);
+ *stack_hi = stackaddr;
+ *stack_lo = (char*)stackaddr - stacksize;
  return;
 # else
 # warning "Getting precise stack size for thread is not supported."