Fix:

error: implicit declaration of function 'puts' is invalid in C99 [-Werror,-Wimplicit-function-declaration]

error: implicitly declaring library function 'exit' with type 'void (int) __attribute__((noreturn))' [-Werror,-Wimplicit-function-declaration]

error: implicitly declaring library function 'malloc' with type 'void *(unsigned long)' [-Werror,-Wimplicit-function-declaration]

error: implicitly declaring library function 'strlen' with type 'unsigned long (const char *)' [-Werror,-Wimplicit-function-declaration]

error: implicit declaration of function 'ioctl' is invalid in C99 [-Werror,-Wimplicit-function-declaration]

error: implicitly declaring library function 'abort' with type 'void (void) __attribute__((noreturn))' [-Werror,-Wimplicit-function-declaration]
--- configure.orig	2007-12-28 21:28:03.000000000 -0600
+++ configure	2020-12-29 21:20:42.000000000 -0600
@@ -23909,6 +23909,7 @@
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 
+#include <stdio.h>
 int
 main ()
 {
@@ -24684,7 +24685,7 @@
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 #include <stdio.h>
-int main () { exit (rename ("conftest.1", "conftest.2")); }
+int main () { return rename("conftest.1", "conftest.2"); }
 _ACEOF
 rm -f conftest$ac_exeext
 if { (ac_try="$ac_link"
@@ -27310,7 +27311,7 @@
     int
     main ()
     {
-      exit (malloc (0) ? 0 : 1);
+      return malloc(0) ? 0 : 1;
     }
 
 _ACEOF
@@ -27391,7 +27392,7 @@
     int
     main ()
     {
-      exit (realloc (0, 0) ? 0 : 1);
+      return realloc(0, 0) ? 0 : 1;
     }
 
 _ACEOF
--- lib/argmatch.c.orig	2007-12-28 19:37:53.000000000 -0600
+++ lib/argmatch.c	2020-12-29 21:19:51.000000000 -0600
@@ -22,6 +22,7 @@
 
 #include <stdio.h>
 #ifdef STDC_HEADERS
+# include <stdlib.h>
 # include <string.h>
 #endif
 
--- lib/path-concat.c.orig	2007-12-28 19:37:54.000000000 -0600
+++ lib/path-concat.c	2020-12-29 21:22:53.000000000 -0600
@@ -31,7 +31,9 @@
 #endif
 #include <sys/types.h>
 
-/* char *malloc (); */
+#ifdef HAVE_STDLIB_H
+# include <stdlib.h>
+#endif
 
 #ifndef DIRECTORY_SEPARATOR
 # define DIRECTORY_SEPARATOR '/'
--- lib/title.c.orig	2007-12-28 19:37:54.000000000 -0600
+++ lib/title.c	2020-12-29 21:28:02.000000000 -0600
@@ -29,6 +29,10 @@
 
 #include <stdio.h>
 
+#ifdef HAVE_STRING_H
+# include <string.h>
+#endif
+
 #if HAVE_VPRINTF || HAVE_DOPRNT || _LIBC
 # if __STDC__
 #  include <stdarg.h>
--- lib/tterm.c.orig	2007-12-28 19:37:54.000000000 -0600
+++ lib/tterm.c	2020-12-29 21:26:23.000000000 -0600
@@ -63,7 +63,7 @@
 # include <termios.h>
 #endif
 
-#ifdef HAVE_SYS_IOCTL
+#ifdef HAVE_SYS_IOCTL_H
 # include <sys/ioctl.h>
 #endif
 
--- lib/obstack.h.orig	2007-12-28 19:37:59.000000000 -0600
+++ lib/obstack.h	2020-12-29 21:41:26.000000000 -0600
@@ -109,6 +109,10 @@
 #ifndef _OBSTACK_H
 #define _OBSTACK_H 1
 
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
--- src/long-options.c.orig	2007-12-28 19:33:58.000000000 -0600
+++ src/long-options.c	2020-12-29 21:44:25.000000000 -0600
@@ -22,6 +22,9 @@
 #endif
 
 #include <stdio.h>
+#ifdef HAVE_STDLIB_H
+# include <stdlib.h>
+#endif
 #include <getopt.h>
 #include "closeout.h"
 #include "long-options.h"