Make the allocators used by malloc and linux_umalloc valgrindable.
Include valgrind headers in the codebase to avoid a build dependency
on valgrind.

Signed-off-by: Piotr Jaroszyński <p.jaroszynski@gmail.com>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

Building the Linux-specific code (tap.o et al) requires external
headers that have proven to be extremely variable across systems,
causing frequent build failures.

Until this situation is rectified, remove the Linux-specific code from
the default (non-Linux build).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Add makefiles, ld scripts and default config for linux platform for
both i386 and x86_64.

Signed-off-by: Piotr Jaroszyński <p.jaroszynski@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>