1.0.17.24: refactor handling of constants in the compiler

1.0.17.24: refactor handling of constants in the compiler

 * Coalesce non-circular lists, bit-vectors, and non-base-strings in the
   file-compiler. (We could do more, but these are the "easy" ones.) Takes
   care of OPTIMIZATIONS #34 in practice: outside the file compiler one can
   still trick the system into similar behaviour, but that seems a fairly
   academic concern.

 * Never go through SYMBOL-VALUE at runtime to fetch the value of a constant
   variable in compiled code.

 * Use (SYMBOL-VALUE <NAME>) as the load-form to dump references to named
   constants into fasls.

 * Signal a continuable error if an attempt to change the SYMBOL-VALUE of a
   constant variable is made.

 * Assignments to undefined variables go through SET, so that one
   cannot accidentally modify a constant by doing something like:

    (defun set-foo (x) (setq foo x))
    (defconstant foo 42)
    (set-foo 13)

 * Gets rid of INFO :VARIABLE :CONSTANT-VALUE, and just uses SYMBOL-VALUE to
   store constant values.

 * Move definition of SB!XC:LAMBDA-LIST-KEYWORDS to be beginning of the build,
   and use it instead of the host LAMBDA-LIST-KEYWORDS where appropriate.

 * Tests.