Change in flashrom[master]: tests: Do not run a test if its driver is not built

[Nico Huber (Code Review)]

Attention is currently required from: Edward O'Callaghan, Anastasia Klimchuk.
Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/55295 )

Change subject: tests: Do not run a test if its driver is not built
......................................................................

Patch Set 4:

(1 comment)

File tests/init_shutdown.c:

https://review.coreboot.org/c/flashrom/+/55295/comment/d260fae4_d5cf0e93 
PS1, Line 35: #if CONFIG_DUMMY == 1
            : void dummy_init_and_shutdown_test_success(void **state)
            : {
            : 	run_lifecycle(state, PROGRAMMER_DUMMY, "bus=parallel+lpc+fwh+spi");
            : }
            : #endif /* CONFIG_DUMMY */
> "yes"/"no" is only used on the user end. Both Meson and the Makefile always use
> `=1` for the `-D` arguments. However, what is rather unfortunate, they only ever
> provide `1` and never `0`. So the only way to use it is useful is indeed with #if.
> :-/

I forgot that we had the same problem with Kconfig in coreboot. It was solved long
ago by a complex macro. It's quite nice, so we should add that to flashrom at some
point:

/*
     * Getting something that works in C and CPP for an arg that may or may
     * not be defined is tricky.  Here, if we have "#define CONFIG_BOOGER 1"
     * we match on the placeholder define, insert the "0," for arg1 and generate
     * the triplet (0, 1, 0).  Then the last step cherry picks the 2nd arg (a one).
     * When CONFIG_BOOGER is not defined, we generate a (... 1, 0) pair, and when
     * the last step cherry picks the 2nd arg, we get a zero.
     */
    #define __ARG_PLACEHOLDER_1 0,
    #define config_enabled(cfg) _config_enabled(cfg)
    #define _config_enabled(value) __config_enabled(__ARG_PLACEHOLDER_##value)
    #define __config_enabled(arg1_or_junk) ___config_enabled(arg1_or_junk 1, 0, 0)
    #define ___config_enabled(__ignored, val, ...) val

#define CONFIG(option) config_enabled(CONFIG_##option)

How does it work? well, that's a riddle even with the comment ^^ (hint: the
comment is not accounting for the last `, 0` which is only necessary to be
C compatible where one always needs at least one variadic argument).

How is it used?

CONFIG(DUMMY)

would expand to 1 iff CONFIG_DUMMY == 1, otherwise (even if CONFIG_DUMMY
is not defined) it expands to 0.