LibC: Add POSIX timer constants

Kernel/Syscalls/sysconf.cpp

@@ -14,6 +14,8 @@ namespace Kernel {
 KResultOr<long> Process::sys$sysconf(int name)
 {
     switch (name) {
+    case _SC_MONOTONIC_CLOCK:
+        return 1;
     case _SC_NPROCESSORS_CONF:
     case _SC_NPROCESSORS_ONLN:
         return Processor::processor_count();

Kernel/UnixTypes.h

@@ -37,6 +37,7 @@
 #define MS_REMOUNT (1 << 5)
 
 enum {
+    _SC_MONOTONIC_CLOCK,
     _SC_NPROCESSORS_CONF,
     _SC_NPROCESSORS_ONLN,
     _SC_OPEN_MAX,