LibC+LibELF: Move ELF definitions from LibC to LibELF

This is needed to avoid including LibC headers in Lagom builds.
Unfortunately, we cannot rely on the build machine to provide a
fully POSIX-compatible ELF header for Lagom builds, so we have to
use our own.

Kernel/Tasks/Process.h

@@ -36,7 +36,7 @@
 #include <Kernel/Tasks/ProcessGroup.h>
 #include <Kernel/Tasks/Thread.h>
 #include <Kernel/UnixTypes.h>
-#include <LibC/elf.h>
+#include <LibELF/ELFABI.h>
 
 namespace Kernel {