[Issue 21938] importC: Support __attribute__ specifiers that could be mapped to D attributes

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21938

--- Comment #4 from Walter Bright <bugzilla at digitalmars.com> ---
For always_inline:

https://github.com/dlang/dmd/pull/15134

--