asm! should catch attempts to use `.intel_syntax` or `.att_syntax` and suggest appropriate options instead

[joshtriplett]

People used to gcc/clang inline assembly may try using the .intel_syntax or .att_syntax directives directly in the assembly string, which can cause issues. Ideally, we should detect attempts to use those directives. Attempting to use .intel_syntax should generate an error stating that that's the default. Attempting to use .att_syntax should generate an error and point to the att_syntax option, ideally with a rustfix-applicable suggestion.

[asquared31415]

Is anyone currently working on this? I would like to do it if not.

[joshtriplett]

@asquared31415 Not to my knowledge, no.

[asquared31415]

@rustbot claim