peval: fix algorithmic behavior of `cons'

peval: fix algorithmic behavior of `cons'

* module/language/tree-il/optimize.scm (peval): Fix treatment of `cons'
  to not process the value twice, leading to n^2 work.  This prevented
  primitives.scm from compiling in a reasonable amount of time, because
  it contained a `(foo ... ,@bar) form that resulted in a long sequence
  of nested conses, and no effort counter was in place as it was not
  within an inlining attempt.