Add The LISP Challenge

This change introduces a 2.5kb program that's comes pretty close so far
to bootstrapping John McCarthy's metacircular evaluator on bare metal.

tool/emacs/cosmo-c-builtins.el

@@ -256,6 +256,7 @@
            "__builtin_lrintf"
            "__builtin_lrintl"
            "__builtin_memcpy"
+           "__builtin_memcmp"
            "__builtin_memset"
            "__builtin_strlen"))
 

tool/emacs/cosmo-c-keywords.el

@@ -126,6 +126,7 @@
         (cosmo
          '("__rbx"
            "__msabi"
+           "offsetof"
            "microarchitecture"
            "targetclones"
            "testonly"

tool/emacs/cosmo-cpp-constants.el

@@ -141,6 +141,7 @@
    "OPEN_MAX"
    "ATEXIT_MAX"
    "IM_FEELING_NAUGHTY"
+   "__REAL_MODE__"
    "__x86__"
    "__i386__"))