- Export the function added in r265456 rather than the non-existent

_rtld_debug_postinit(). [1]
- Use __compiler_membar() instead of inline asm in _r_debug_state() and
  _r_debug_postinit(). [2]

Pointy hat to:	markj [1]
Reported by:	attilio [2]
Discussed with:	kib
X-MFC-With:	r265456

libexec/rtld-elf/Symbol.map

@@ -30,5 +30,5 @@ FBSDprivate_1.0 {
     _rtld_atfork_post;
     _rtld_addr_phdr;
     _rtld_get_stack_prot;
-    _rtld_debug_postinit;
+    _r_debug_postinit;
 };

libexec/rtld-elf/rtld.c

@@ -3551,7 +3551,7 @@ r_debug_state(struct r_debug* rd, struct link_map *m)
      * even when marked __noinline.  However, gdb depends on those
      * calls being made.
      */
-    __asm __volatile("" : : : "memory");
+    __compiler_membar();
 }
 
 /*
@@ -3564,7 +3564,7 @@ _r_debug_postinit(struct link_map *m)
 {
 
 	/* See r_debug_state(). */
-	__asm __volatile("" : : : "memory");
+	__compiler_membar();
 }
 
 /*