error.h not found on alpine about crun

[tiborvass]

I managed to get it to compile on alpine with tiborvass/libocispec@3cda24a
and tiborvass@7323c9a although I'm not super satisfied with replacing secure_getenv with getenv when secure_getenv is missing.

[giuseppe]

hi thanks for the patches. I've applied the patch to libocispec and to crun.

When secure_getenv is missing, I think we can use the version defined in gnulib: http://git.savannah.gnu.org/cgit/gnulib.git/tree/lib/secure_getenv.c, that is distributed under LGPL3+.

I've changed your patch to drop the #define secure_getenv getenv bit, please let me know if it still looks fine to you.

I've opened a PR here: #140

[tiborvass]

Thanks @giuseppe!