Merge dtksh patches from one of the CDE developers (#85)

This merges some fixes to support building dtksh with -DBUILD_DTKSH.
These patches were sent through private email from the CDE developer
Chase. The reason these patches were submitted is because Chase wishes
to include ksh in CDE as an up-to-date git submodule. Quote from Chase:
"... my priority is to get your new version into our code as a git
 submodule, and do it quickly before our code bases differ too widely."

Link to CDE project for anyone interested:
https://sourceforge.net/projects/cdesktopenv/

Although the patches were privately discussed, there are some public
emails on the CDE mailing list (links shortened due to long URLs):
ksh-chaos thread:   https://bit.ly/3hjJ83b
dtksh alias thread: https://bit.ly/3hkzKfJ

The main fix is for suid_exec, which is now told that /usr/dt is a
valid directory to run from via preprocessor flags. A patch for
Shift-JIS was also submitted, but it isn't in this commit because it
isn't an effective fix for the existing Shift-JIS bugs. I will be
giving that patch some more testing.

From: Chase <nicetrynsa@protonmail.ch>
Co-authored by: Johnothan King <johnothanking@protonmail.com>

src/cmd/ksh93/include/nval.h

@@ -33,6 +33,10 @@
 #include	<cdt.h>
 #include	<option.h>
 
+#ifdef BUILD_DTKSH
+#include       <hash.h>
+#endif
+
 /* for compatibility with old hash library */
 #define Hashtab_t	Dt_t
 #define HASH_BUCKET	1
@@ -111,6 +115,9 @@ struct Namdecl
 /* This defines the attributes for an attributed name-value pair node */
 struct Namval
 {
+#if BUILD_DTKSH
+	HASH_HEADER;                    /* space for hash library */
+#endif
 	Dtlink_t	nvlink;		/* space for cdt links */
 	char		*nvname;	/* pointer to name of the node */
 #if _ast_sizeof_pointer == 8