Add more out of memory checks (re: 18529b88) (#192)

The referenced commit neglected to add checks for strdup() calls.
That calls malloc() as well, and is used a lot.

This commit switches to another strategy: it adds wrapper functions
for all the allocation macros that check if the allocation
succeeded, so those checks don't need to be done manually.

src/cmd/ksh93/include/defs.h,
src/cmd/ksh93/sh/init.c:
- Add sh_malloc(), sh_realloc(), sh_calloc(), sh_strdup(),
  sh_memdup() wrapper functions with success checks. Call nospace()
  to error out if allocation fails.
- Update new_of() macro to use sh_malloc().
- Define new sh_newof() macro to replace newof(); it uses
  sh_realloc().

All other changed files:
- Replace the relevant calls with the wrappers.
- Remove now-redundant success checks from 18529b88.
- The ERROR_PANIC error message calls are updated to inclusive-or
  ERROR_SYSTEM into the exit code argument, so libast's error()
  appends the human-readable version of errno in square brackets.
  See src/lib/libast/man/error.3

src/cmd/ksh93/edit/history.c:
- Include "defs.h" to get access to the wrappers even if KSHELL is
  not defined.
- Since we're here, fix a compile error that occurred with KSHELL
  undefined by updating the type definition of hist_fname[] to
  match that of history.h.

src/cmd/ksh93/bltins/enum.c:
- To get access to sh_newof(), include "defs.h" instead of
  <shell.h> (note that "defs.h" includes <shell.h> itself).

src/cmd/ksh93/Mamfile:
- enum.c: depend on defs.h instead of shell.h.
- enum.o: add an -I. flag in the compiler invocation so that defs.h
  can find its subsequent includes.

src/cmd/builtin/pty.c:
- Define one outofmemory() function and call that instead of
  repeating the error message call.
- outofmemory() never returns, so remove superfluous exit handling.

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

src/cmd/ksh93/sh/subshell.c

@@ -188,7 +188,7 @@ void sh_subfork(void)
 	pid_t pid;
 	char *trap = shp->st.trapcom[0];
 	if(trap)
-		trap = strdup(trap);
+		trap = sh_strdup(trap);
 	/* see whether inside $(...) */
 	if(sp->pipe)
 		sh_subtmpfile(shp->comsub);
@@ -307,9 +307,7 @@ Namval_t *sh_assignok(register Namval_t *np,int add)
 			return(np);
 	}
 	/* first two pointers use linkage from np */
-	lp = (struct Link*)malloc(sizeof(*np)+2*sizeof(void*));
-	if(!lp)
-		sh_outofmemory();
+	lp = (struct Link*)sh_malloc(sizeof(*np)+2*sizeof(void*));
 	memset(lp,0, sizeof(*mp)+2*sizeof(void*));
 	lp->node = np;
 	if(!add &&  nv_isvtree(np))
@@ -609,7 +607,7 @@ Sfio_t *sh_subshell(Shell_t *shp,Shnode_t *t, volatile int flags, int comsub)
 			}
 		}
 #endif /* _lib_fchdir */
-		sp->pwd = (shp->pwd?strdup(shp->pwd):0);
+		sp->pwd = (shp->pwd?sh_strdup(shp->pwd):0);
 		sp->mask = shp->mask;
 		sh_stats(STAT_SUBSHELL);
 		/* save trap table */
@@ -617,12 +615,10 @@ Sfio_t *sh_subshell(Shell_t *shp,Shnode_t *t, volatile int flags, int comsub)
 		shp->st.otrap = savst.trap;
 		if((nsig=shp->st.trapmax)>0 || shp->st.trapcom[0])
 		{
-			savsig = malloc(nsig * sizeof(char*));
-			if(!savsig)
-				sh_outofmemory();
+			savsig = sh_malloc(nsig * sizeof(char*));
 			/*
 			 * the data is, usually, modified in code like:
-			 *	tmp = buf[i]; buf[i] = strdup(tmp); free(tmp);
+			 *	tmp = buf[i]; buf[i] = sh_strdup(tmp); free(tmp);
 			 * so shp->st.trapcom needs a "deep copy" to properly save/restore pointers.
 			 */
 			for (isig = 0; isig < nsig; ++isig)
@@ -630,7 +626,7 @@ Sfio_t *sh_subshell(Shell_t *shp,Shnode_t *t, volatile int flags, int comsub)
 				if(shp->st.trapcom[isig] == Empty)
 					savsig[isig] = Empty;
 				else if(shp->st.trapcom[isig])
-					savsig[isig] = strdup(shp->st.trapcom[isig]);
+					savsig[isig] = sh_strdup(shp->st.trapcom[isig]);
 				else
 					savsig[isig] = NULL;
 			}