Refactor #82270 as lint instead of an error
This PR fixes several issues with #82270 which generated an error when `.intel_syntax` or `.att_syntax` was used in inline assembly:
- It is now a warn-by-default lint instead of an error.
- The lint only triggers on x86. `.intel_syntax` and `.att_syntax` are only valid on x86.
- The lint no longer provides machine-applicable suggestions for two reasons:
- These changes should not be made automatically since changes to assembly code can be very subtle.
- The template string is not always just a string: it can contain macro invocation (`concat!`), raw strings, escape characters, etc.
cc ``@asquared31415``
02b27cd79e