Defining strlcpy here clashes on macOS, which has some compiler magic
around their strlcpy declaration. Fix this by inverting the check
to declare the prototype only if we are on __GLIBC__. As uClibc may
define __GLIBC__ as well, check for absence of its __UCLIBC__.

This is in-line with what Linux has been doing since 0215d59b15
("tools lib: Reinstate strlcpy() header guard with __UCLIBC__").

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>