Nearly all instances of nasm_fatal() and nasm_panic() take a flags
argument of zero. Simplify the code by making nasm_fatal and
nasm_panic default to no flags, and add an alternate version if flags
really are desired. This also means that every call site doesn't have
to initialize a zero argument.
Furthermore, ERR_NOFILE is now often not necessary, as the error code
will no longer cause a null reference if there is no current
file. Therefore, we can remove many instances of ERR_NOFILE which only
deprives the user of information.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>