https://github.com/FeralInteractive/gamemode/commit/4934191b1928ef695c3e8af21e75781f8591745f
https://bugs.gentoo.org/863995

From: =?UTF-8?q?Nyikos=20Zolt=C3=A1n?= <nyikoszoltan0@gmail.com>
Date: Wed, 10 Aug 2022 19:56:59 +0200
Subject: [PATCH] Fix building when pidfd_open is available

On glibc2.36 pidfd_open was made available, but it needs an include
--- a/common/common-pidfds.c
+++ b/common/common-pidfds.c
@@ -58,6 +58,8 @@ static int pidfd_open(pid_t pid, unsigned int flags)
 {
 	return (int)syscall(__NR_pidfd_open, pid, flags);
 }
+#else
+#include <sys/pidfd.h>
 #endif
 
 /* pidfd functions */