Fix the setsid-after-vfork configure check to avoid implicit
declarations of wait, exit.  This ensures that the outcome of the
check does not change with compilers which do not support implicit
function declarations.

Submitted upstream:

  <https://tug.org/pipermail/tex-live/2023-January/048833.html>

diff -up texlive-base-20220321/source/texk/xdvik/configure.c99-4 texlive-base-20220321/source/texk/xdvik/configure
--- texlive-base-20220321/source/texk/xdvik/configure.c99-4	2023-01-31 09:04:59.026325806 +0100
+++ texlive-base-20220321/source/texk/xdvik/configure	2023-01-31 09:05:14.250169332 +0100
@@ -16406,6 +16406,9 @@ else $as_nop
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
 #endif
+#ifdef HAVE_SYS_WAIT_H
+#include <sys/wait.h>
+#endif
 #ifdef HAVE_VFORK_H
 #include <vfork.h>
 #endif
@@ -16427,7 +16430,7 @@ main (void)
 
     while (wait(&status) != child)
       ;
-    exit(
+    _exit(
 	 /* Was there some problem with vforking?  */
 	 child < 0
 
diff -up texlive-base-20220321/source/texk/xdvik/m4/xdvi-func-setsid-in-fork.m4.c99-4 texlive-base-20220321/source/texk/xdvik/m4/xdvi-func-setsid-in-fork.m4
--- texlive-base-20220321/source/texk/xdvik/m4/xdvi-func-setsid-in-fork.m4.c99-4	2023-01-31 08:45:31.417794738 +0100
+++ texlive-base-20220321/source/texk/xdvik/m4/xdvi-func-setsid-in-fork.m4	2023-01-31 08:45:43.901652431 +0100
@@ -22,6 +22,9 @@ AC_DEFUN([XDVI_FUNC_SETSID_IN_VFORK],
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
 #endif
+#ifdef HAVE_SYS_WAIT_H
+#include <sys/wait.h>
+#endif
 #ifdef HAVE_VFORK_H
 #include <vfork.h>
 #endif]],
@@ -40,7 +43,7 @@ AC_DEFUN([XDVI_FUNC_SETSID_IN_VFORK],
 
     while (wait(&status) != child)
       ;
-    exit(
+    _exit(
 	 /* Was there some problem with vforking?  */
 	 child < 0