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

src/cmd/ksh93/data/builtins.c

@@ -135,18 +135,14 @@ const struct shtable3 shtab_builtins[] =
 #include SHOPT_CMDLIB_HDR
 #else
 	CMDLIST(basename)
-	CMDLIST(chmod)
+	CMDLIST(cat)
+	CMDLIST(cp)
+	CMDLIST(cut)
 	CMDLIST(dirname)
 	CMDLIST(getconf)
-	CMDLIST(head)
-	CMDLIST(mkdir)
-	CMDLIST(logname)
-	CMDLIST(cat)
-	CMDLIST(cmp)
-	CMDLIST(cut)
-	CMDLIST(uname)
-	CMDLIST(wc)
-	CMDLIST(sync)
+	CMDLIST(ln)
+	CMDLIST(mktemp)
+	CMDLIST(mv)
 #if !_std_malloc && !_AST_std_malloc
 	CMDLIST(vmstate)  /* vmstate only works with vmalloc */
 #endif