rt: Add FIXME's about future changes to LLVM's __morestack impl

Author: brson

src/rt/arch/i386/morestack.S

@@ -19,6 +19,8 @@
 #define MORESTACK               __morestack
 #endif
 
+// FIXME: Future LLVM patches remove these 8 alignment bytes from
+// the function prologue in order to match gcc's behavior
 #define ALIGNMENT 8
 #define RETURN_OFFSET   7
 

src/rt/rust_task.cpp

@@ -588,6 +588,9 @@ rust_task::del_stack() {
 
 void
 rust_task::record_stack_limit() {
+    // FIXME: Future LLVM patches expect us to add an additional 256 bytes
+    // here so that, if the frame size is < 256 it can generate the
+    // comparison against esp directly, instead of some offset from esp
     record_sp(stk->data + RED_ZONE_SIZE);
 }
 //