targets: explicitly mark the stack as NOLOAD

This prevents it from being of type PROGBITS in lld 9, it should always
be NOBITS. It should fix the following error in lld 9:

    ROM segments are non-contiguous

targets/gameboy-advance.ld

@@ -32,7 +32,7 @@ SECTIONS
     /* Put the stack at the bottom of RAM, so that the application will
      * crash on stack overflow instead of silently corrupting memory.
      * See: http://blog.japaric.io/stack-overflow-protection/ */
-    .stack :
+    .stack (NOLOAD) :
     {
         . = ALIGN(4);
         . += _stack_size;