New selection of default libcmd /opt/ast/bin built-ins

Note that this is only about the /opt/ast/bin built-in commands,
not about the regular pathless builtins such as printf.
To use these, either add /opt/ast/bin to your $PATH or use a
command like 'builtin cp'. As usual, --man provides info.

Removed as defaults for lack of convincing advantages over the OS's
external commands:
- chmod, cmp, head, logname, mkdir, sync, uname, wc

Remain as useful defaults:
- basename, cat, cut, dirname. These are commonly used in
  performance-sensitive code paths in scripts and having them as
  built-ins can be good for performance.
- getconf: This is the only interface to some libast internals that
  is available to ksh. It's also has better functionality than most
  OS-shipped 'getconf' commands, e.g., it can list and query all
  the configuration values.

Added as defaults:
- cp, ln, mv: Having these built in can speed up scripts that
  manage files. Also the AST versions have extended functionality
  (see cp --man, etc.).
- mktemp: External mktemp commands vary too widely and are
  incompatible, but it's important that scripts can securely make
  temporary files, so it's good to ship a known interface to this
  functionality.

As a result, the statically linked ksh binary is very slightly
smaller than before.

Resolves: https://github.com/ksh93/ksh/issues/349

NEWS

@@ -3,6 +3,12 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2021-12-16:
+
+- Changed the default selection of compiled-in /opt/ast/bin built-in libcmd
+  command to: basename, cat, cp, cut, dirname, getconf, ln, mktemp, mv.
+  Add /opt/ast/bin to your $PATH to use these. Type 'cp --man', etc. for info.
+
 2021-12-13:
 
 - Fixed a bug introduced on 2020-08-09 that prevented '.' and '..' from