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.

Cleanup and centralize the Makefile system even more.
Fix a gcc 4.3 incompatibility in memdisk (definition of strlen).

Move source files out of the root directory; the root is a mess and
has become virtually unmaintainable.  The Syslinux core now lives in
core/; the Linux and generic utilities has moved into utils/, and
copybs.com has moved into dos/; it had to go somewhere, and it seemed
as good a place as any.

If the variable GZIP exists in the environment, overriding it in the
Makefile exports it into the environment, causing failures:

gzip -cd syslogo.ppm.gz | \
		../ppmtolss16 \#000000=0 \#d0d0d0=7 \#f6f6f6=15	\
		> syslogo.lss
gzip.gz: No such file or directory
204480 pixels, 25715 bytes, (74.85% compression)

Use $GZIPPROG instead.