Fix many compiler warnings and remove unused variables (#191)

Most of these changes remove unused variables, functions and labels
to fix -Wunused compiler warnings. Somewhat notable changes:

src/cmd/ksh93/bltins/print.c:
- Removed the unused 'neg' variable.
  Patch from ksh2020: https://github.com/att/ast/pull/725

src/cmd/ksh93/bltins/sleep.c:
- Initialized ns to fix three -Wsometimes-uninitialized warnings.

src/cmd/ksh93/edit/{emacs,vi}.c:
- Adjust strncpy size to fix two -Wstringop-truncation warnings.

src/cmd/ksh93/include/shell.h:
- The NOT_USED macro caused many -Wunused-value warnings,
  so it has been replaced with ksh2020's macro:
  19d0620a

src/cmd/ksh93/sh/expand.c:
- Removed an unnecessary 'ap = ' since 'ap' is never read
  between stakseek and stakfreeze.

src/cmd/ksh93/edit/vi.c: refresh():
- Undef this function's 'w' macro at the end of it to stop it
  potentially interfering with future code changes.

src/cmd/ksh93/sh/nvdisc.c,
src/lib/libast/misc/magic.c,
src/lib/libast/regex/regsubexec.c,
src/lib/libast/sfio/sfpool.c,
src/lib/libast/vmalloc/vmbest.c:
- Fixed some indentation to silence -Wmisleading-indentation
  warnings.

src/lib/libast/include/ast.h:
- For clang, now only suppress hundreds of -Wparentheses warnings
  as well as a few -Wstring-plus-int warnings.
  Clang's -Wparentheses warns about things like
  	if(foo = bar())
  which assigns to foo and checks the assigned value.
  Clang wants us to change this into
  	if((foo = bar()))
  Clang's -Wstring-plus-int warns about things like
  	"string"+x
  where x is an integer, e.g. "string"+3 represents the string
  "ing". Clang wants us to change that to
  	"string"[3]
  The original versions represent a perfectly valid coding style
  that was common in the 1980s and 1990s and is not going to change
  in this historic code base. (gcc does not complain about these.)

Co-authored-by: Martijn Dekker <martijn@inlv.org>

src/cmd/ksh93/sh/expand.c

@@ -65,11 +65,6 @@
 #   define GLOB_AUGMENTED	0
 #endif
 
-#define GLOB_RESCAN 1
-#define globptr()	((struct glob*)membase)
-
-static struct glob	 *membase;
-
 static char *nextdir(glob_t *gp, char *dir)
 {
 	Shell_t	*shp = sh_getinterp();
@@ -143,7 +138,7 @@ static int scantree(Dt_t *tree, const char *pattern, struct argnod **arghead)
 	{
 		if(strmatch(cp=nv_name(np),pattern))
 		{
-			ap = (struct argnod*)stakseek(ARGVAL);
+			(void)stakseek(ARGVAL);
 			stakputs(cp);
 			ap = (struct argnod*)stakfreeze(1);
 			ap->argbegin = NIL(char*);

src/cmd/ksh93/sh/init.c

@@ -383,16 +383,6 @@ static void put_cdpath(register Namval_t* np,const char *val,int flags,Namfun_t
 }
 
 #ifdef _hdr_locale
-    /*
-     * This function needs to be modified to handle international
-     * error message translations
-     */
-    static char* msg_translate(const char* catalog, const char* message)
-    {
-	NOT_USED(catalog);
-	return((char*)message);
-    }
-
     /* Trap for LC_ALL, LC_CTYPE, LC_MESSAGES, LC_COLLATE and LANG */
     static void put_lang(Namval_t* np,const char *val,int flags,Namfun_t *fp)
     {
@@ -731,13 +721,6 @@ static void put_lastarg(Namval_t* np,const char *val,int flags,Namfun_t *fp)
 	np->nvenv = 0;
 }
 
-static int hasgetdisc(register Namfun_t *fp)
-{
-        while(fp && !fp->disc->getnum && !fp->disc->getval)
-                fp = fp->next;
-	return(fp!=0);
-}
-
 /*
  * store the most recent value for use in .sh.match
  * treat .sh.match as a two dimensional array
@@ -1034,7 +1017,6 @@ static const Namdisc_t SH_MATH_disc  = { 0, 0, get_math, 0, setdisc_any, create_
 	return((char*)np->nvalue.cp);
     }
     static const Namdisc_t NSPACE_disc	= {  0, 0, get_nspace };
-    static Namfun_t NSPACE_init	= {  &NSPACE_disc, 1};
 #endif /* SHOPT_NAMESPACE */
 
 #ifdef _hdr_locale

src/cmd/ksh93/sh/io.c

@@ -387,14 +387,6 @@ struct Match
 	char	*base;
 };
 
-static int matchf(void *handle, char *ptr, size_t size)
-{
-	struct Match *mp = (struct Match*)handle;
-	mp->offset += (ptr-mp->base);
-	return(1);
-}
-
-
 static struct fdsave	*filemap;
 static short		filemapsize;
 

src/cmd/ksh93/sh/jobs.c

@@ -1092,8 +1092,6 @@ int job_kill(register struct process *pw,register int sig)
 int job_hup(struct process *pw, int sig)
 {
 	struct process	*px;
-	pid_t	pid;
-	int	r;
 	NOT_USED(sig);
 	if(pw->p_pgrp == 0 || (pw->p_flag & P_DISOWN))
 		return(0);

src/cmd/ksh93/sh/nvdisc.c

@@ -947,11 +947,11 @@ int nv_clone(Namval_t *np, Namval_t *mp, int flags)
 	if(flags&NV_APPEND)
 		return(1);
 	if(mp->nvsize == size)
-	        nv_setsize(mp,nv_size(np));
+		nv_setsize(mp,nv_size(np));
 	if(mp->nvflag == flag)
-	        mp->nvflag = (np->nvflag&~(NV_MINIMAL))|(mp->nvflag&NV_MINIMAL);
-		if(nv_isattr(np,NV_EXPORT))
-			mp->nvflag |= (np->nvflag&NV_MINIMAL);
+		mp->nvflag = (np->nvflag&~(NV_MINIMAL))|(mp->nvflag&NV_MINIMAL);
+	if(nv_isattr(np,NV_EXPORT))
+		mp->nvflag |= (np->nvflag&NV_MINIMAL);
 	if(mp->nvalue.cp==val && !nv_isattr(np,NV_INTEGER))
 	{
 		if(np->nvalue.cp && np->nvalue.cp!=Empty && (flags&NV_COMVAR) && !(flags&NV_MOVE))

src/cmd/ksh93/sh/xec.c

@@ -70,7 +70,6 @@ static void	coproc_init(Shell_t*, int pipes[]);
 static void	*timeout;
 static char	nlock;
 static char	pipejob;
-static char	nopost;
 static int	restorefd;
 
 struct funenv