Clean up the handling of firmware selection inside the Makefiles.

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

This variable indicates whether or nor the files are compiled for EFI.
The lack of it lead the Makefiles to forget to add some compilation
options specific to EFI.

Signed-off-by: Sylvain Gault <sylvain.gault@gmail.com>

A lot more items have identical dependencies; regroup.  Certain items make
more sense to build first; resequence.  Group library dependencies before
COM32 directories

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>

Resort and collapse the list; add libutil to dep lib

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>

From: Chong Lu <Chong.Lu at windriver.com>

There might be an error when parallel build:

[snip]
cp: cannot create directory `tmp/sysroots/x86_64-linux/usr/share/
syslinux/com32/include/gplinclude': No such file or directory
make[4]: *** [install] Error 1
make[3]: *** [gpllib] Error 2
[snip]

This is a potential issue. In ${S}/com32/gpllib/Makefile file,
install target wants to copy $(SRC)/../gplinclude to
$(INSTALLROOT)$(COM32DIR)/include/ directory, but in ${S}/com32/lib/Makefile
file, the install target will remove $(INSTALLROOT)$(COM32DIR)/include
directory. We need to do com32/lib first.

The patch make com32/gpllib depends on com32/lib to fix this issue.

Upstream-Status: Pending

Signed-off-by: Chong Lu <Chong.Lu at windriver.com>
Signed-off-by: Robert Yang <liezhi.yang at windriver.com>
Signed-off-by: Gene Cumm <gene.cumm@gmail.com>

Fixed:
cp -r syslinux-6.01/com32/libupload/*.h image/usr/share/syslinux/com32/include/
[snip]
rm -rf image/usr/share/syslinux/com32/include
[snip]
cp: cannot create regular file `image/usr/share/syslinux/com32/include/serial.h': No such file or directory

The cp is happened in the "libupload" dir, while "rm -fr" is happend in
"lib" dir, let "libupload" depend "lib" will fix the problem.

Signed-off-by: Robert Yang <liezhi.yang at windriver.com>
Signed-off-by: Gene Cumm <gene.cumm@gmail.com>

Lua shall be one of the latest module to build as it requires some other
components to be built before.

Prior this patch, it was impossible to make a parallel build when "j"
was greater than 26.

This patch fix the ordering and allow a "make -j"  of com32 directory.

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>

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>