Fix:

error: type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int [-Wimplicit-int]
error: call to undeclared library function 'exit' with type 'void (int) __attribute__((noreturn))'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
--- configure
+++ configure
@@ -4337,6 +4337,7 @@ _ACEOF
 cat confdefs.h >>conftest.$ac_ext
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
+#include <stdlib.h>
 #include <sys/stat.h>
 int
 main ()
@@ -6275,9 +6276,10 @@ cat confdefs.h >>conftest.$ac_ext
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 
+#include <stdlib.h>
 #include <sys/types.h>
 #include <regex.h>
-main() {
+int main() {
 	regex_t patbuf;
 	exit (regcomp (&patbuf, "/hello/", 0) != 0);
 }

