Now that we have multiple firmware backends it no longer makes sense
to write object files to the same directory as their source. A better
solution is to write the object files to a per-firmware directory
under a top-level object directory.

The top-level object directory can be specified on the command-line
with the O= variable, e.g. make O=/tmp/obj. If no top-level object
directory is specified an 'obj' directory is created in the top-level
of the Syslinux source repository.

All the existing make targets continue to work as before, however now
they apply to all firmware backends, e.g. 'make installer' will build
the BIOS, 32-bit EFI and 64-bit EFI installers and place them under
$(OBJ)/bios, $(OBJ)/efi32 and $(OBJ)/efi64 respectively.

Note unlike every other bit of Syslinux, the gpxe objects are still
kept in the src directory, e.g. gpxe/src, since gpxe is only required
by the BIOS backend.

It is possible to specify a make target for a specific firmware or
list of firmware with the following syntax,

    make [firmware[,firmware]] [target[,target]]

To clean the object directory for just the BIOS firmware type,

      'make bios clean'

To build both the 32-bit and 64-bit EFI installers type,

     'make efi32 efi64 installer'

Since the Syslinux make infrastructure is now more complex a new file
doc/building.txt has been created to explain how to build Syslinux.

The top-level Makefile now exports some make variables for use in
module Makefiles,

    - topdir - the top-level source directory of the Syslinux
      repository, e.g. /usr/src/syslinux

    - objdir - the top-level object directory for the firmware
      backend currently being built, e.g. /obj/syslinux/bios

    - SRC - the source directory in the Syslinux repository for the
      module currently being built,
      e.g. /usr/src/syslinux/com32/libupload

    - OBJ - the object directory for the module currently being
      built, e.g. /obj/syslinux/bios/com32/libupload

Since we're rewriting the Makefile infrastructure anyway it seemed
like a good idea to add parallel support. By writing subdirectories as
prequisites for make targets the objects in those subdirectories can
be built in parallel.

Signed-off-by: Matt Fleming <matt.fleming@intel.com>

Move the MCONFIG files into a mk/ directory and give them more
descriptive names.

This is purely a cosmetic change to make the 'include' directives a
bit more coherent by making it obvious exactly which MCONFIG file
we're including. For example, in com32/lua/src/Makefile we exchange
the line,

	include ../../MCONFIG

for the much more comprehensible,

	include $(MAKEDIR)/com32.mk

Signed-off-by: Matt Fleming <matt.fleming@linux.intel.com>

Without the include, .ppm.gz to .lss messes up as $(GZIPPROG) is
not expanded properly

We really don't want people to write code without using the library,
so just remove these obsolete and no longer functional samples.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

Fix missing -M from NASM dependency generation calls; adopt the
uniform stanza "-M -DDEPEND" even for sites that were already correct.

Also, use ">" not ">>" for obvious reasons...

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Unify dependency generation and move common rules into
MCONFIG.embedded.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Unify common pieces to "embedded" targets (those that produce code
that runs neither in the host nor in a com32 environment); this fixes
the broken sample/ directory Makefile.