[Outlining] Sort sequences by order appeared in function (WebAssembly#7164)

During function reconstruction, a walker iterates thru each instruction
of a function, incrementing a counter to find matching sequences. As a
result, the sequences of a function must be sorted by smallest start
index, otherwise reconstruction will miss outlining a repeat sequence.

I considered making a test for this commit, but the sort wasn't needed
until the tests started running on GitHub infra. I'm not sure what
specific architecture is causing the discrepancy in vector ordering, but
let's introduce the sort to be safe.

Author: ashleynh

src/passes/Outlining.cpp

@@ -364,11 +364,20 @@ struct Outlining : public Pass {
                    seqByFunc.end(),
                    keys.begin(),
                    [](auto pair) { return pair.first; });
-    for (auto funcName : keys) {
-      auto* func = module->getFunction(funcName);
-      ReconstructStringifyWalker reconstruct(module, func);
-      reconstruct.sequences = std::move(seqByFunc[funcName]);
-      reconstruct.doWalkFunction(func);
+    for (auto func : keys) {
+      // During function reconstruction, a walker iterates thru each instruction
+      // of a function, incrementing a counter to find matching sequences. As a
+      // result, the sequences of a function must be sorted by
+      // smallest start index, otherwise reconstruction will miss outlining a
+      // repeat sequence.
+      std::sort(seqByFunc[func].begin(),
+                seqByFunc[func].end(),
+                [](OutliningSequence a, OutliningSequence b) {
+                  return a.startIdx < b.startIdx;
+                });
+      ReconstructStringifyWalker reconstruct(module, module->getFunction(func));
+      reconstruct.sequences = std::move(seqByFunc[func]);
+      reconstruct.doWalkFunction(module->getFunction(func));
     }
   }