[Instrumentation] Fix EdgeCounts vector size in SetBranchWeights

SetBranchWeights() calculates the size of the EdgeCounts vector
using OutEdges.Size(), but this is an under-estimate with coroutines.

Use the number of successors, as the vector will be indexed by
the result of the GetSuccessorNumber() function.

This crashes in 18.1, but somehow doesn't in main. Still, it looks
like the fix is applicable to both.

Fixes llvm#97962

llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp

@@ -1624,7 +1624,9 @@ void PGOUseFunc::setBranchWeights() {
 
     // We have a non-zero Branch BB.
     unsigned Size = BBCountInfo.OutEdges.size();
-    SmallVector<uint64_t, 2> EdgeCounts(Size, 0);
+    unsigned SuccessorCount = BB.getTerminator()->getNumSuccessors();
+
+    SmallVector<uint64_t, 2> EdgeCounts(SuccessorCount, 0);
     uint64_t MaxCount = 0;
     for (unsigned s = 0; s < Size; s++) {
       const PGOUseEdge *E = BBCountInfo.OutEdges[s];