Add accessors for current_task and safe_restore in TLS (#36064)

In code which may be compiled against one Julia version but then gets
loaded in another (e.g. due to an update), it is problematic to directly
access members of jl_ptls_t, as this structure frequently changes
between Julia versions

The existing accessor function `jl_get_current_task` helps to avoid this,
so make it public.

Note that the public macro `jl_current_task` exist, but since macros are
compiled into the code which includes `julia.h`, they do not deal with the
situation described above.

No alternatives currently exist for `jl_get_safe_restore` and
`jl_set_safe_restore`.

src/julia.h

@@ -2077,6 +2077,11 @@ typedef struct {
 #define jl_current_task (jl_get_ptls_states()->current_task)
 #define jl_root_task (jl_get_ptls_states()->root_task)
 
+JL_DLLEXPORT jl_value_t *jl_get_current_task(void);
+
+JL_DLLEXPORT jl_jmp_buf *jl_get_safe_restore(void);
+JL_DLLEXPORT void jl_set_safe_restore(jl_jmp_buf *);
+
 // codegen interface ----------------------------------------------------------
 // The root propagation here doesn't have to be literal, but callers should
 // ensure that the return value outlives the MethodInstance

src/julia_internal.h

@@ -1021,7 +1021,6 @@ JL_DLLEXPORT jl_value_t *(jl_array_data_owner)(jl_array_t *a);
 JL_DLLEXPORT int jl_array_isassigned(jl_array_t *a, size_t i);
 
 JL_DLLEXPORT uintptr_t jl_object_id_(jl_value_t *tv, jl_value_t *v) JL_NOTSAFEPOINT;
-JL_DLLEXPORT jl_value_t *jl_get_current_task(void);
 JL_DLLEXPORT void jl_set_next_task(jl_task_t *task);
 
 // -- synchronization utilities -- //

src/task.c

@@ -612,6 +612,18 @@ JL_DLLEXPORT jl_value_t *jl_get_current_task(void)
     return (jl_value_t*)ptls->current_task;
 }
 
+JL_DLLEXPORT jl_jmp_buf *jl_get_safe_restore(void)
+{
+    jl_ptls_t ptls = jl_get_ptls_states();
+    return (jl_value_t*)ptls->safe_restore;
+}
+
+JL_DLLEXPORT void jl_set_safe_restore(jl_jmp_buf *sr)
+{
+    jl_ptls_t ptls = jl_get_ptls_states();
+    ptls->safe_restore = sr;
+}
+
 #ifdef JL_HAVE_ASYNCIFY
 JL_DLLEXPORT jl_ucontext_t *task_ctx_ptr(jl_task_t *t)
 {