[M] Change in flashrom[master]: tests: Mock the mode_t variant of open

[Anastasia Klimchuk (Code Review)]

Attention is currently required from: Evan Benn.

Anastasia Klimchuk has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/69263 )

Change subject: tests: Mock the mode_t variant of open
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Patch Set 7:

(2 comments)

File tests/io_mock.h:

https://review.coreboot.org/c/flashrom/+/69263/comment/73dd77c8_11a3484d 
PS4, Line 37: #include <fcntl.h>
> this one is posix, and posix says: `The <fcntl.h> header shall define the mode_t` […]

I will try to test

File tests/tests.c:

https://review.coreboot.org/c/flashrom/+/69263/comment/5344f4cd_5e133b3f 
PS4, Line 103: mode_t mode = 0;
             : 	if (flags & O_CREAT) {
             : 		va_list ap;
             : 		va_start(ap, flags);
             : 		mode = va_arg(ap, mode_t);
             : 		va_end(ap);
             : 	}
> It has to be in the varargs function. […]

open64 and open64_2 are needed for some of the environments, so we can't remove them. Let's keep as is then.