Kernel: Alias `_SC_PAGE_SIZE` to `_SC_PAGESIZE`

Both of those are specified by POSIX.

Kernel/API/POSIX/unistd.h

@@ -53,6 +53,7 @@ enum {
 #define _SC_NPROCESSORS_ONLN _SC_NPROCESSORS_ONLN
 #define _SC_OPEN_MAX _SC_OPEN_MAX
 #define _SC_PAGESIZE _SC_PAGESIZE
+#define _SC_PAGE_SIZE _SC_PAGESIZE
 #define _SC_HOST_NAME_MAX _SC_HOST_NAME_MAX
 #define _SC_TTY_NAME_MAX _SC_TTY_NAME_MAX
 #define _SC_GETPW_R_SIZE_MAX _SC_GETPW_R_SIZE_MAX