apply patch from https://github.com/davidrg/mars_nwe/issues/1#issuecomment-2259477604

opt/comm.c

@@ -21,6 +21,8 @@
 #define ENV_UNXCOMM    "UNXCOMM"
 
 #ifdef LINUX
+# include <unistd.h>
+# include <string.h>
 # define DEFAULT_COMM   "/pipes/unxcomm"
 #else
 # ifdef  DEFAULT_UNC

opt/sendm.c

@@ -12,6 +12,8 @@
 
 #define ENV_UNXCOMM    "UNXSENDM"
 #ifdef LINUX
+# include <unistd.h>
+# include <string.h>
 # define DEFAULT_COMM   "/pipes/unxsendm"
 # else
 # define DEFAULT_COMM   "p:/unxsendm"

opt/unxcomm.c

@@ -8,6 +8,7 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <sys/time.h>

opt/unxsendm.c

@@ -5,6 +5,7 @@
  */
 
 #include <stdio.h>
+#include <unistd.h>
 #include <fcntl.h>
 #include <sys/time.h>
 #include <sys/types.h>
@@ -36,7 +37,7 @@ int main(int argc, char *argv[])
     FILE *f;
     char path[MAXARGLEN+200];
     buf[size]='\0';
-    sprintf(path, "/usr/sbin/sendmail %s", buf);
+    sprintf(path, "/usr/bin/sendmail %s", buf);
     f=popen(path, "w");
     if (NULL != f) {
       write(1, "+++++\n", 6);