Add a FIXME comment to mention it's a temporary fix.

Author: weiguozhi

llvm/lib/Analysis/LoopInfo.cpp

@@ -60,6 +60,8 @@ static cl::opt<bool, true>
 
 bool Loop::isLoopInvariant(const Value *V) const {
   if (const Instruction *I = dyn_cast<Instruction>(V)) {
+    // FIXME: this is semantically inconsistent. We're tracking a proper fix in
+    // issue #149604.
     // If V is a pointer to stack object and F is a coroutine function, then V
     // may not be loop invariant because the ramp function and resume function
     // have different stack frames.