Reimplement C output generation. There's now a procedural layer for

Reimplement C output generation.  There's now a procedural layer for
generating C code, which gives significantly greater control over the
output formatting.  Code using the layer is simpler and clearer than
what it replaces.

Additionally, the output no longer uses DEFUN, EXFUN, etc., instead
generating ANSI C.  This allows the generated code to be used with the
(unreleased) v15 microcode.