compile_file uses the tertiary return value of
COMPILE-FILE to tell whether the compilation succeeded.
At least one lisp (Clisp) returns a positive value if
there are warnings, so compile_file thinks the
compilation failed when actually there weren't errors.
A comment in the code (src/transs.lisp) says
;; If the compiler encountered errors, don't set
;; indicate that we found errors. Is this what we want?
I think the answer is "no".