Apart from some definitions and includes, this patch also removes the LESS -T
call so that other implementations of LESS (such as busybox) work as well.
diff -upr a/usr.bin/mandoc/chars.c b/usr.bin/mandoc/chars.c
--- a/usr.bin/mandoc/chars.c	2020-02-13 19:16:03.000000000 +0300
+++ b/usr.bin/mandoc/chars.c	2020-10-15 20:28:37.865510442 +0300
@@ -16,6 +16,7 @@
  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
+#include <sys/cdefs.h>
 #include <sys/types.h>
 
 #include <assert.h>
diff -upr a/usr.bin/mandoc/dba.c b/usr.bin/mandoc/dba.c
--- a/usr.bin/mandoc/dba.c	2017-02-09 21:26:17.000000000 +0300
+++ b/usr.bin/mandoc/dba.c	2020-10-15 20:14:07.403360262 +0300
@@ -17,6 +17,7 @@
  * Allocation-based version of the mandoc database, for read-write access.
  * The interface is defined in "dba.h".
  */
+#include <sys/cdefs.h>
 #include <sys/types.h>
 #include <endian.h>
 #include <errno.h>
diff -upr a/usr.bin/mandoc/dbm.c b/usr.bin/mandoc/dbm.c
--- a/usr.bin/mandoc/dbm.c	2019-07-02 01:43:03.000000000 +0300
+++ b/usr.bin/mandoc/dbm.c	2020-10-15 20:15:44.217488475 +0300
@@ -31,6 +31,10 @@
 #include "dbm_map.h"
 #include "dbm.h"
 
+#ifndef EFTYPE
+#define EFTYPE 79
+#endif
+
 struct macro {
 	int32_t	value;
 	int32_t	pages;
diff -upr a/usr.bin/mandoc/dbm_map.c b/usr.bin/mandoc/dbm_map.c
--- a/usr.bin/mandoc/dbm_map.c	2017-02-09 21:26:17.000000000 +0300
+++ b/usr.bin/mandoc/dbm_map.c	2020-10-15 20:16:40.740563806 +0300
@@ -36,6 +36,10 @@
 #include "dbm_map.h"
 #include "dbm.h"
 
+#ifndef EFTYPE
+#define EFTYPE 79
+#endif
+
 static struct stat	 st;
 static char		*dbm_base;
 static int		 ifd;
diff -upr a/usr.bin/mandoc/html.c b/usr.bin/mandoc/html.c
--- a/usr.bin/mandoc/html.c	2020-04-20 15:59:24.000000000 +0300
+++ b/usr.bin/mandoc/html.c	2020-10-15 20:31:07.733706743 +0300
@@ -18,6 +18,7 @@
  * Common functions for mandoc(1) HTML formatters.
  * For use by individual formatters and by the main program.
  */
+#include <sys/cdefs.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 
diff -upr a/usr.bin/mandoc/main.c b/usr.bin/mandoc/main.c
--- a/usr.bin/mandoc/main.c	2020-04-03 01:10:27.000000000 +0300
+++ b/usr.bin/mandoc/main.c	2020-10-15 20:36:12.432111094 +0300
@@ -405,8 +405,10 @@ main(int argc, char *argv[])
 		}
 		if (search.arch == NULL)
 			search.arch = getenv("MACHINE");
+#ifdef MACHINE
 		if (search.arch == NULL)
 			search.arch = MACHINE;
+#endif
 		if (outmode == OUTMODE_ONE)
 			search.firstmatch = 1;
 	}
@@ -1183,7 +1185,6 @@ spawn_pager(struct tag_files *tag_files,
 	char		*argv[MAX_PAGER_ARGS];
 	const char	*pager;
 	char		*cp;
-	size_t		 cmdlen;
 	int		 argc, use_ofn;
 	pid_t		 pager_pid;
 
@@ -1218,18 +1219,6 @@ spawn_pager(struct tag_files *tag_files,
 	/* For more(1) and less(1), use the tag file. */
 
 	use_ofn = 1;
-	if (*tag_files->tfn != '\0' && (cmdlen = strlen(argv[0])) >= 4) {
-		cp = argv[0] + cmdlen - 4;
-		if (strcmp(cp, "less") == 0 || strcmp(cp, "more") == 0) {
-			argv[argc++] = mandoc_strdup("-T");
-			argv[argc++] = tag_files->tfn;
-			if (tag_target != NULL) {
-				argv[argc++] = mandoc_strdup("-t");
-				argv[argc++] = tag_target;
-				use_ofn = 0;
-			}
-		}
-	}
 	if (use_ofn)
 		argv[argc++] = tag_files->ofn;
 	argv[argc] = NULL;
diff -upr a/usr.bin/mandoc/mandoc_ohash.c b/usr.bin/mandoc/mandoc_ohash.c
--- a/usr.bin/mandoc/mandoc_ohash.c	2015-10-19 21:58:20.000000000 +0300
+++ b/usr.bin/mandoc/mandoc_ohash.c	2020-10-15 20:22:30.788037370 +0300
@@ -14,6 +14,7 @@
  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
+#include <sys/cdefs.h>
 #include <sys/types.h>
 #include <stddef.h>
 #include <stdint.h>
diff -upr a/usr.bin/mandoc/mandoc_xr.c b/usr.bin/mandoc/mandoc_xr.c
--- a/usr.bin/mandoc/mandoc_xr.c	2017-07-03 00:17:12.000000000 +0300
+++ b/usr.bin/mandoc/mandoc_xr.c	2020-10-15 20:22:48.871060409 +0300
@@ -14,6 +14,7 @@
  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
+#include <sys/cdefs.h>
 #include <sys/types.h>
 
 #include <assert.h>
diff -upr a/usr.bin/mandoc/mansearch.c b/usr.bin/mandoc/mansearch.c
--- a/usr.bin/mandoc/mansearch.c	2019-07-02 01:43:03.000000000 +0300
+++ b/usr.bin/mandoc/mansearch.c	2020-10-15 20:23:05.476081586 +0300
@@ -16,6 +16,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <sys/cdefs.h>
 #include <sys/mman.h>
 #include <sys/types.h>
 
diff -upr a/usr.bin/mandoc/roff.c b/usr.bin/mandoc/roff.c
--- a/usr.bin/mandoc/roff.c	2020-04-08 14:54:14.000000000 +0300
+++ b/usr.bin/mandoc/roff.c	2020-10-15 20:23:23.988105223 +0300
@@ -17,6 +17,7 @@
  *
  * Implementation of the roff(7) parser for mandoc(1).
  */
+#include <sys/cdefs.h>
 #include <sys/types.h>
 
 #include <assert.h>
diff -upr a/usr.bin/mandoc/tag.c b/usr.bin/mandoc/tag.c
--- a/usr.bin/mandoc/tag.c	2020-04-19 19:26:11.000000000 +0300
+++ b/usr.bin/mandoc/tag.c	2020-10-15 20:23:39.327124832 +0300
@@ -17,6 +17,7 @@
  * Functions to tag syntax tree nodes.
  * For internal use by mandoc(1) validation modules only.
  */
+#include <sys/cdefs.h>
 #include <sys/types.h>
 
 #include <assert.h>