[libsmi] Supressing the implicit function declaration warning

C99 - C11 does not allow implicit function declarations by default, this stops lib/yang-complex-types.c from compiling. Pulling the [changes](https://github.com/Slenderman00/LibSMI/commit/eb7ddd9d9a4db4f5e4fbd9bdb37665...) from https://github.com/Slenderman00/LibSMI fixes the issue. My fork simply suppresses the error.

Joar Heimonen Developer UiT ITA Joar.me