bpo-42598: Fix implicit function declarations in configure (GH-23690) (GH-23756)

This is invalid in C99 and later and is an error with some compilers
(e.g. clang in Xcode 12), and can thus cause configure checks to
produce incorrect results.
(cherry picked from commit 674fa0a740151e0416c9383f127b16014e805990)

Co-authored-by: Joshua Root <jmr@macports.org>

1 files changed, 7 insertions, 6 deletions

diff --git a/configure b/configure
index 2d379feb4b7..ed969c55b35 100755
--- a/configure
+++ b/configure
@@ -11072,10 +11072,10 @@ else
       main() {
         pthread_attr_t attr;
         pthread_t id;
-        if (pthread_attr_init(&attr)) exit(-1);
-        if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) exit(-1);
-        if (pthread_create(&id, &attr, foo, NULL)) exit(-1);
-        exit(0);
+        if (pthread_attr_init(&attr)) return (-1);
+        if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) return (-1);
+        if (pthread_create(&id, &attr, foo, NULL)) return (-1);
+        return (0);
       }
 _ACEOF
 if ac_fn_c_try_run "$LINENO"; then :
@@ -15083,7 +15083,7 @@ else
   int main()
   {
 	/* Success: exit code 0 */
-        exit((((wchar_t) -1) < ((wchar_t) 0)) ? 0 : 1);
+        return ((((wchar_t) -1) < ((wchar_t) 0)) ? 0 : 1);
   }
 
 _ACEOF
@@ -15464,7 +15464,7 @@ else
 
 int main()
 {
-	exit(((-1)>>3 == -1) ? 0 : 1);
+	return (((-1)>>3 == -1) ? 0 : 1);
 }
 
 _ACEOF
@@ -15934,6 +15934,7 @@ else
 /* end confdefs.h.  */
 
 #include <poll.h>
+#include <unistd.h>
 
 int main()
 {