Bug 1658809 - add non-executable stack markers to aarch64 asm; r=glandium

Noticed this while preparing some other patches, might as well address it.

Differential Revision: https://phabricator.services.mozilla.com/D86850

xpcom/reflect/xptcall/md/unix/xptcinvoke_asm_aarch64.s

@@ -78,4 +78,4 @@ _NS_InvokeByIndex:
 
             .size _NS_InvokeByIndex, . - _NS_InvokeByIndex
 
-
+            .section .note.GNU-stack, "", @progbits ; .previous

xpcom/reflect/xptcall/md/unix/xptcstubs_asm_aarch64.s

@@ -47,3 +47,5 @@ SharedStub:
             .cfi_endproc
 
             .size SharedStub, . - SharedStub
+
+            .section .note.GNU-stack, "", @progbits ; .previous