Change in flashrom[staging]: Fix linking with libpayload

[Nico Huber (Code Review)]

Nico Huber has posted comments on this change. ( https://review.coreboot.org/18738 )

Change subject: Fix linking with libpayload
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Patch Set 6:

(1 comment)

https://review.coreboot.org/#/c/18738/6/helpers.c
File helpers.c:

https://review.coreboot.org/#/c/18738/6/helpers.c@95
PS6, Line 95: #if defined(__DJGPP__)
> Hmm, I wonder if it's still useful to have a check for glibc compatibility

These feature_test_macros(7) work the other way around: You define
them before including any header file and the header file declares
the guarded functions (see dmi.c for an example). So in case of
glibc, we can just assume that we have strnlen().

I've done some more testing and investigation: The HAVE_STRNLEN
check was introduced for older BSDs in 23e10b8. But I guess it
was copied from examples that assume GNU autotools are used. It's
working because the linker seems to ignore the conflicting imple-
mentation.

I'll extend the `!defined(HAVE_STRNLEN)` with a libpayload guard.
Just removing it would break these older BSDs again.