Kernel: Generate a coredump file when a process crashes

When a process crashes, we generate a coredump file and write it in
/tmp/coredumps/.

The coredump file is an ELF file of type ET_CORE.
It contains a segment for every userspace memory region of the process,
and an additional PT_NOTE segment that contains the registers state for
each thread, and a additional data about memory regions
(e.g their name).

Kernel/Forward.h

@@ -30,6 +30,7 @@ namespace Kernel {
 
 class BlockDevice;
 class CharacterDevice;
+class CoreDump;
 class Custody;
 class Device;
 class DiskCache;