Address some warnings.

src/block_alloc.h

src/encode.c

src/peep.c

src/post_modules/Nettle/aead.cmod

src/post_modules/Nettle/cipher.cmod

src/post_modules/Nettle/hogweed.cmod

src/post_modules/Nettle/mac.cmod

src/post_modules/Nettle/nettle.cmod

src/stack_allocator.c