Kernel: Add _SC_PAGESIZE to sysconf

This unbreaks the gcc and binutils ports.
Previously, when _SC_PAGESIZE was missing, these packages opted to
use their own versions of getpagesize which made their build fail
because of conflicting definitions of the function.

Kernel/Syscalls/sysconf.cpp

@@ -24,6 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <Kernel/Arch/i386/CPU.h>
 #include <Kernel/Process.h>
 
 namespace Kernel {
@@ -34,6 +35,8 @@ long Process::sys$sysconf(int name)
     case _SC_NPROCESSORS_CONF:
     case _SC_NPROCESSORS_ONLN:
         return Processor::processor_count();
+    case _SC_PAGESIZE:
+        return PAGE_SIZE;
     default:
         return -EINVAL;
     }

Kernel/UnixTypes.h

@@ -58,6 +58,7 @@
 enum {
     _SC_NPROCESSORS_CONF,
     _SC_NPROCESSORS_ONLN,
+    _SC_PAGESIZE,
 };
 
 #define PERF_EVENT_MALLOC 1