The concat object can get out of sequence so don't optimize a repeat.

Under some situation the optimized repeat expression can get out
of sync while it is being processed this causes the code to
reference freed memory. This happens when the repeat expression
is converted to an unsigned integer, but the repeat expression
is used in a different path. It was easier to just remove the
optimization then track down the convoluted call sequence that
was causing this and then figure out what needed to be fixed.
The repeat expression must be constant, so is likely not too
complicated so this optimization is very minor and should not
be missed.
(cherry picked from commit 3259354d29)

PExpr.h

@@ -183,7 +183,6 @@ class PEConcat : public PExpr {
       std::valarray<unsigned>tested_widths_;
 
       PExpr*repeat_;
-      NetExpr*repeat_expr_;
 };
 
 /*