LibC+Kernel: Start implementing sysconf

For now, only the non-standard _SC_NPROCESSORS_CONF and
_SC_NPROCESSORS_ONLN are implemented.

Use them to make ninja pick a better default -j value.
While here, make the ninja package script not fail if
no other port has been built yet.

Ports/ninja/patches/nproc.patch

@@ -1,13 +0,0 @@
-diff --git a/src/util.cc b/src/util.cc
-index ae94d34..72cf501 100644
---- a/src/util.cc
-+++ b/src/util.cc
-@@ -476,7 +476,7 @@ int GetProcessorCount() {
-   GetNativeSystemInfo(&info);
-   return info.dwNumberOfProcessors;
- #else
--  return sysconf(_SC_NPROCESSORS_ONLN);
-+  return 1;  // FIXME: serenity way of saying sysconf(_SC_NPROCESSORS_ONLN);
- #endif
- }
-