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/include/defs.h

@@ -290,8 +290,6 @@ struct shared
 /* error exits from various parts of shell */
 #define	NIL(type)	((type)0)
 
-#define new_of(type,x)	((type*)malloc((unsigned)sizeof(type)+(x)))
-
 #define exitset()	(sh.savexit=sh.exitval)
 
 #ifndef SH_DICT
@@ -367,7 +365,6 @@ extern Sfdouble_t	sh_mathfun(Shell_t*, void*, int, Sfdouble_t*);
 extern int		sh_outtype(Shell_t*, Sfio_t*);
 extern char 		*sh_mactry(Shell_t*,char*);
 extern int		sh_mathstd(const char*);
-extern void		sh_outofmemory(void);
 extern void		sh_printopts(Shopt_t,int,Shopt_t*);
 extern int 		sh_readline(Shell_t*,char**,volatile int,int,ssize_t,long);
 extern Sfio_t		*sh_sfeval(char*[]);
@@ -392,6 +389,15 @@ extern int 		sh_whence(char**,int);
     extern Namval_t	*sh_fsearch(Shell_t*,const char *,int);
 #endif /* SHOPT_NAMESPACE */
 
+/* malloc related wrappers */
+extern void		*sh_malloc(size_t size);
+extern void		*sh_realloc(void *ptr, size_t size);
+extern void		*sh_calloc(size_t nmemb, size_t size);
+extern char		*sh_strdup(const char *s);
+extern void		*sh_memdup(const void *s, size_t n);
+#define new_of(type,x)	((type*)sh_malloc((unsigned)sizeof(type)+(x)))
+#define sh_newof(p,t,n,x)	((p)?(t*)sh_realloc((char*)(p),sizeof(t)*(n)+(x)):(t*)sh_calloc(1,sizeof(t)*(n)+(x)))
+
 #define URI_RFC3986_UNRESERVED "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~"
 
 #ifndef ERROR_dictionary