https://bugs.gentoo.org/952945
--- a/configure.ac
+++ b/configure.ac
@@ -121,11 +121,11 @@ AC_RUN_IFELSE([AC_LANG_SOURCE([[
 #define _GNU_SOURCE 1
 #endif
 #include <features.h>
-void main(void) {
+int main(void) {
 #if _XOPEN_SOURCE >= 500
-exit(0); /* UNIX98 compatible */
+return 0; /* UNIX98 compatible */
 #else
-exit(-1); /* not UNIX98 compatible */
+return 1; /* not UNIX98 compatible */
 #endif
 }
 ]])],
@@ -339,12 +339,12 @@ if test "$config_alsa_driver" = "yes"; then
     AC_LANG_PUSH([C])
     AC_RUN_IFELSE([AC_LANG_SOURCE([[
         #include <alsa/asoundlib.h>
-        void main(void) {
+        int main(void) {
             /* ensure backward compatibility */
             #if !defined(SND_LIB_MAJOR) && defined(SOUNDLIB_VERSION_MAJOR)
             #define SND_LIB_MAJOR SOUNDLIB_VERSION_MAJOR
             #endif
-            exit(SND_LIB_MAJOR);
+            return(SND_LIB_MAJOR);
         }
     ]])],
     alsa_major=0,
@@ -353,12 +353,12 @@ if test "$config_alsa_driver" = "yes"; then
     )
     AC_RUN_IFELSE([AC_LANG_SOURCE([[
         #include <alsa/asoundlib.h>
-        void main(void) {
+        int main(void) {
             /* ensure backward compatibility */
             #if !defined(SND_LIB_MINOR) && defined(SOUNDLIB_VERSION_MINOR)
             #define SND_LIB_MINOR SOUNDLIB_VERSION_MINOR
             #endif
-            exit(SND_LIB_MINOR);
+            return(SND_LIB_MINOR);
         }
     ]])],
     alsa_minor=0,
@@ -367,12 +367,12 @@ if test "$config_alsa_driver" = "yes"; then
     )
     AC_RUN_IFELSE([AC_LANG_SOURCE([[
         #include <alsa/asoundlib.h>
-        void main(void) {
+        int main(void) {
             /* ensure backward compatibility */
             #if !defined(SND_LIB_SUBMINOR) && defined(SOUNDLIB_VERSION_SUBMINOR)
             #define SND_LIB_SUBMINOR SOUNDLIB_VERSION_SUBMINOR
             #endif
-            exit(SND_LIB_SUBMINOR);
+            return(SND_LIB_SUBMINOR);
         }
     ]])],
     alsa_subminor=0,