Do not schedule BBs before the entry point

Summary:
SPEC CPU2006 perlbench triggered a bug in our heuristic block
reordering algorithm where a hot edge that targets the entry point (as in a
recursive tail call) would make us try to allocate the call site before the
function entry point. Since we don't update function addresses yet, moving the
entry point will corrupt the program. This patch fixes this.

(cherry picked from FBD2562528)

bolt/BinaryFunction.cpp

@@ -595,7 +595,7 @@ void BinaryFunction::optimizeLayout(bool DumpLayout) {
     int I = 0, J = 0;
 
     // Case 1: BBSrc and BBDst are the same. Ignore this edge
-    if (BBSrc == BBDst)
+    if (BBSrc == BBDst || BBDst == Entry)
       continue;
 
     // Case 2: Both BBSrc and BBDst are already allocated