INIT: remove proto, ratz (re: 46593a89, 6137b99a); major cleanup

This takes another step towards cleaning up the build system. We
now do not even pretend to be theoretically compatible with
pre-1989 K&R C compilers or with C++ compilers. In practice, this
had already been broken for many years due to bit rot.

Commit 46593a89 already removed the license handling enormity that
depended on proto, so now we can cleanly remove it altogether. But
we do need to leave some backwards compatibility stubs to keep the
build system compatible with older AST code; it should remain
possible to build older ksh versions with the current build system
(the bin/ and src/cmd/INIT/ directories) for testing purposes.

So as of now there is no more __MANGLE__d rubbish in your generated
header files. This is only about a quarter of a century overdue...

This commit also includes a huge amount of code cleanup to remove
thousands of unused K&R C fallbacks and other cruft, particularly
in libast. This code base should now be a little easier to
understand for people who are familiar with a modern(ish) C
standard.

ratz is now also removed; this was a standalone and simplified 2005
version of gunzip. As of 6137b99a, none of our code uses it, even
theoretically. And the real g(un)zip is now everywhere.

src/cmd/INIT/proto.c, src/cmd/INIT/ratz.c:
- Removed.

COPYRIGHT:
- Remove zlib license; this only applied to ratz.

bin/package, src/cmd/INIT/package.sh:
- Related cleanups.
- Unset LC_ALL before invoking a new shell, respecting the user's
  locale again and avoiding multibyte character corruption on the
  command line.

src/cmd/INIT/proto.sh:
- Add stub for backwards compatibility with Mamfiles that depend on
  proto. It does nothing but pass input without modification and is
  now installed as the new arch/*/bin/proto by src/cmd/INIT/Mamfile.

src/cmd/INIT/iffe.sh:
- Ignore the proto-related -e (--package) and -p (--prototyped)
  options; keep parsing them for backwards compatibility.
- Trim the macros passed to every test to their standard C
  versions, removing K&R C and C++ versions. These are now
  considered to be for backwards compatibility only.

src/cmd/INIT/iffe.tst:
- Remove proto(1) mangling code.
  By the way, iffe can be regression-tested as follows:
        $ bin/package use   # set up environment in a child shell
        $ regress src/cmd/INIT/iffe.tst
        $ exit              # leave package environment

src/cmd/INIT/make.probe, src/cmd/INIT/probe.win32:
- Remove code to handle C++.

src/lib/libast/features/common:
- As in iffe.sh above, trim macros designed for compatibility with
  C++ and ancient C compilers to their standard C versions and
  comment that they are for backwards compatibility with AST code.
  This is needed to keep all the old ast and ksh code compiling.

src/cmd/ksh93/sh/init.c,
src/cmd/ksh93/sh/name.c:
- Clarify libshell ABI compatibility function versions of macros.
  A "proto workaround" comment in the original code mislead me into
  thinking this had something to do with the removed proto(1), but
  it's unrelated. Call the workaround macro BYPASS_MACRO instead.

src/cmd/ksh93/include/defs.h:
- sh_sigcheck() macro: allow &sh as an argument: parenthesise shp.

src/cmd/ksh93/sh/nvtype.c:
- Remove unused nv_mkstruct() function. (re: d0a5cab1)

**/features/*:
- Remove obsolete iffe 'set prototyped' option.

**/Mamfile:
- Remove all references to the ast/prototyped.h header.
- Remove all use of the proto command. Simply copy instead.

*** 850-ish source files: ***
- Remove all '#pragma prototyped' directives.
- Remove all C++ compat code conditional upon defined(__cplusplus).
- Remove all use of the _ARG_ macro, which on standard C expands to
  its argument:
        #define _ARG_(x)        x
  (on K&R C, it expanded to nothing)
- Remove all use of _BEGIN_EXTERNS_ and _END_EXTERNS_ macros (empty
  on standard C; this was for C++ compatibility)
- Reduce all #if __STD_C (standard code) #else (K&R code) #endif
  blocks to the standard code only, without use of the macro.
- Same for _STD_ macro which seems to have had the same function.
- Change all instances of 'Void_t' to standard 'void'.

src/cmd/ksh93/include/regress.h

@@ -18,7 +18,6 @@
 *                  David Korn <dgk@research.att.com>                   *
 *                                                                      *
 ***********************************************************************/
-#pragma prototyped
 /*
  * David Korn
  * AT&T Labs