Kernel: Implement _SC_OPEN_MAX

Author: https://github.com/Lubrsi
Commit: 721788943d
Pull-request: https://github.com/SerenityOS/serenity/pull/3454
Reviewed-by: https://github.com/bugaevc

Libraries/LibC/unistd.h

@@ -174,11 +174,13 @@ enum {
     _SC_NPROCESSORS_CONF,
     _SC_NPROCESSORS_ONLN,
     _SC_PAGESIZE,
+    _SC_OPEN_MAX,
 };
 
 #define _SC_NPROCESSORS_CONF _SC_NPROCESSORS_CONF
 #define _SC_NPROCESSORS_ONLN _SC_NPROCESSORS_ONLN
 #define _SC_PAGESIZE _SC_PAGESIZE
+#define _SC_OPEN_MAX _SC_OPEN_MAX
 
 long sysconf(int name);