stappers and xl0 pointed out that gnu make sets some variables, so ?=
is ineffective in some cases where we use it.. Cross-compilation
requires that some variables can be overridden in the
src/$(ARCH)/Config file, so include that file _after_ utility program
variables are set.

for "echo -e" on the host system.

suitable "echo -e" substitute.

implement the -e option.

(Thanks to Jim McQuillan for this suggestion.)

inside gPXE.

Experimentation reveals that gcc ignores -mrtd for the implicit
arithmetic functions (e.g. __udivdi3), but not for the implicit
memcpy() and memset() functions.  Mark the implicit arithmetic
functions with __attribute__((cdecl)) to compensate for this.

(Note: we cannot mark with with __cdecl, because we define __cdecl to
incorporate regparm(0) as well.)

Even though it is only currently used for rom-o-matic.net code,
it is good to make sure it gets built, and that the parsing code
is working.

bin/%.bin target.

This reverts commit 9dc2515d7e.

I want "make" to actually build something.

"boot" command to attempt booting from within the command shell, fall back
to shell if boot fails for any reason.

used on RTL8139 cards).