Fix compilation if sys/sysctl.h is not present

Glibc 2.32 removes sys/sysctl.h as it is no longer needed. This commit uses
__has_include to check whether the header exists and only includes it if it
does.

Author: jrsnen

libavutil/cpu.c

@@ -39,8 +39,11 @@
 #include <sys/param.h>
 #endif
 #include <sys/types.h>
+
+#if __has_include(<sys/sysctl.h>)
 #include <sys/sysctl.h>
 #endif
+#endif
 #if HAVE_UNISTD_H
 #include <unistd.h>
 #endif