Add a check for the getpeereid() function in macOS

config/check_getpeereid.c

@@ -0,0 +1,13 @@
+#include <sys/types.h>
+#include <unistd.h>
+
+int main()
+{
+    if (0) {
+        int socket = 0;
+        uid_t euid = 0;
+        gid_t egid = 0;
+        getpeereid(socket, &euid, &egid);
+    }
+    return 0;
+}