Another round of accumulated minor fixes and cleanups

Only notable changes listed below.

**/Mamfile:
- Do not bother redirecting standard error for 'cmp -s' to
  /dev/null. Normally, 'cmp -s' on Linux, macOS, *BSD, or Solaris
  do not not print any message. If it does, something unusual is
  going on and I would want to see the message.
- Since we now require a POSIX shell, we can use '!'.

src/cmd/ksh93/include/defs.h,
src/cmd/ksh93/sh/init.c:
- Remove SH_TYPE_PROFILE symbol, unused after the removal of the
  SHOPT_PFSH code. (re: eabd6453)

src/cmd/ksh93/sh/io.c:
- piperead(), slowread(): Replace redundant sffileno() calls by
  the variables already containing their results. (re: 50d342e4)

src/cmd/ksh93/bltins/mkservice.c,
rc/lib/libcmd/vmstate.c:
- If these aren't compiled, define a stub function to silence the
  ranlib(1) warning that the .o file does not contain symbols.

src/cmd/ksh93/sh/parse.c

@@ -376,7 +376,6 @@ static Shnode_t	*makelist(Lex_t *lexp, int type, Shnode_t *l, Shnode_t *r)
  * entry to shell parser
  * Flag can be the union of SH_EOF|SH_NL
  */
-
 void	*sh_parse(Sfio_t *iop, int flag)
 {
 	register Shnode_t	*t;
@@ -507,7 +506,6 @@ Shnode_t *sh_dolparen(Lex_t* lp)
 /*
  * remove temporary files and stacks
  */
-
 void	sh_freeup(void)
 {
 	if(sh.st.staklist)
@@ -520,7 +518,6 @@ void	sh_freeup(void)
  * decrease reference count for each stack in function list when flag<=0
  * stack is freed when reference count is zero
  */
-
 void sh_funstaks(register struct slnod *slp,int flag)
 {
 	register struct slnod *slpold;
@@ -542,7 +539,6 @@ void sh_funstaks(register struct slnod *slp,int flag)
  *	list & [ cmd ]
  *	list [ ; cmd ]
  */
-
 static Shnode_t	*sh_cmd(Lex_t *lexp, register int sym, int flag)
 {
 	register Shnode_t	*left, *right;
@@ -1199,7 +1195,6 @@ static struct argnod *assign(Lex_t *lexp, register struct argnod *ap, int type)
  *	case ... in ... esac
  *	begin ... end
  */
-
 static Shnode_t	*item(Lex_t *lexp,int flag)
 {
 	register Shnode_t	*t;
@@ -1896,7 +1891,6 @@ static struct ionod	*inout(Lex_t *lexp,struct ionod *lastio,int flag)
 /*
  * convert argument chain to argument list when no special arguments
  */
-
 static struct argnod *qscan(struct comnod *ac,int argn)
 {
 	register char **cp;