Fix compiler-macro interaction with LOAD-TIME-VALUE and CONSTANTP.

When CONSTANTP is supplied an &environment object from the compiler
macro it can determine forms involving MACROLET to be constant, but
such forms are problematic for LOAD-TIME-VALUE and its null lexical
environment execution requirements.

test/simple

@@ -364,3 +364,11 @@ characters if there's a match."
            (regex-replace-all (create-scanner "\\p{even}") "abcd" "+")
            (regex-replace-all (create-scanner "\\p{true}") "abcd" "+")))
    '("+b+d" "a+c+" "++++")))
+
+(macrolet ((z () "(a)*b"))
+  (equalp (multiple-value-list (scan (z) "xaaabd"))
+          (list 1 5 #(3) #(4))))
+
+(macrolet ((z () "[^b]*b"))
+  (equalp (multiple-value-list (scan-to-strings (z)  "aaabd"))
+          (list "aaab" #())))