Instruction mismatch errors have been held until the last assembly
pass in case changed %if statements cause a code path to be elided in
subsequent passes. However, it is confusing to the user if error
messages aren't shown if another error terminates assembly.
Use the already existing mechanism for warnings to hold the messages
unless another error terminates assembly.
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
4709cfe493