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>

The Linux kernel puts the stop word at the beginning of the relocation
list (the list is processed backwards); Syslinux puts the stop word at
the beginning of the relocation list (the list is processed forwards.)

Missed that change when syncing with the kernel version.

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

Sync the relocs tool with the Linux kernel.  The new version of this
tool correctly verifies that any absolute symbol is either listed as
allowed absolute or is listed as relative.

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

gcc 4.6 warns on variables set but not used, so remove them.

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

This directory contains builttime tools, so they don't need to be
installed anywhere.

This fixes "make install-all".

Reported-by: Dag Wieers <dag@wieers.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

Create new .gitignore files and add generated files to them.

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

Handle R_386_NONE, which apparently can end up being generated by
binutils in certain circumstances involving sections being removed
completely.

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

Allow relocs.c to sort linker-assigned absolute symbols into true
absolute and relative symbols based on regular expressions.

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

Add missing file com32/tools/Makefile from earlier checkins.  I really
need to pay better attention here...

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