test/c_lib: Skip strerror invalid input test for EXTERNAL_LIBC

Passing an invalid errno value to strerror is undefined behavior in
POSIX. While all Zephyr-specific C libraries may be required to return a
specific value, we can't hold an external C library to that standard.

Signed-off-by: Keith Packard <keithp@keithp.com>
1 file changed