SB-EXT:DESCRIBE-COMPILER-POLICY and local policies

[Tobias C. Rittweiler]

* The docstring of SB-EXT:DESCRIBE-COMPILER-POLICY should be updated with an example
   of what the SPEC argument can be used for.

* It should additionally take an environment as a second &optional parameter, so you can do

     (defun foo (x)
        (declare (optimize speed))
        (macrolet ((print-policy (&environment env)
                            (sb-ext:describe-compiler-policy nil env)))
           (print-policy))
        ...)

   At the moment you can get that behaviour approximated by using

       (print (sb-cltl2:declaration-information 'optimize env))

[Tobias C. Rittweiler (tcr)]

How should the lambda-list for DESCRIBE-COMPILER-POLICY should look like?

Can we get rid of the current &OPTIONAL SPEC argument?

[Tobias C. Rittweiler (tcr)]

I meanwhile figured out that the purpose of the SPEC argument is probably
to see how the dependent qualities change according to SPEC.

If DESCRIBE-COMPILER-POLICY takes a lexenv, that's not strictly necessary
anymore as

  (describe-compiler-policy '((speed 3) (safety 1)))

would be equivalent to

  (macrolet ((print-policy (&environment e)
                       (describe-compiler-policy-from-lexenv e)
                       nil))
     (declare (optimize (speed 3) (safety 1)))
     (print-policy))

That interface would probably suck, though.

The attached patch simply adds an additional &optional parameter for the lexenv.