configure.in: promote some C warnings to errors
configure.in: promote some C warnings to errors

Promote some C warnings to errors, especially ones relating to missing
prototypes.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm