Suppress warnings in certain configuration and fix x86_64 build
This patch declares prototypes for _nettle_gcm_init_key() and _nettle_gcm_hash() as needed in gcm-internal.h and it fixes preprocessor directive in gcm.c.
This patch declares prototypes for _nettle_gcm_init_key() and _nettle_gcm_hash() as needed in gcm-internal.h and it fixes preprocessor directive in gcm.c.