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

Kernel/Syscalls/sysconf.cpp

@@ -37,6 +37,8 @@ long Process::sys$sysconf(int name)
         return Processor::processor_count();
     case _SC_PAGESIZE:
         return PAGE_SIZE;
+    case _SC_OPEN_MAX:
+        return max_open_file_descriptors();
     default:
         return -EINVAL;
     }

Kernel/UnixTypes.h

@@ -60,6 +60,7 @@ enum {
     _SC_NPROCESSORS_CONF,
     _SC_NPROCESSORS_ONLN,
     _SC_PAGESIZE,
+    _SC_OPEN_MAX
 };
 
 #define PERF_EVENT_MALLOC 1