[clang-format] Improve support for AttributeMacro

[jaredgrubb]

clang-format doesn't handle AttributeMacro in all the same ways as __attribute__ macros (which is means to emulate). For example, here are some things that don't format great, especially in ObjC:

// Attributes don't get a space between them sometimes:
- (id)init ATTRIBUTE_MACRO(X)ATTRIBUTE_MACRO;
- (id)init ATTRIBUTE_MACRO(X)__attribute__((X));

// @interface should go on its own line
ATTRIBUTE_MACRO(X) ATTRIBUTE_MACRO @interface Foo
@end

// Style: ColumnWidth smaller to require wrapping
// This indentation is really ugly.
ATTRIBUTE_MACRO
   ATTRIBUTE_MACRO(X)
   @interface Foo
@end

[jaredgrubb]

Note that I have a patch in review on Discourse (it's been up a while):
https://reviews.llvm.org/D145262#inline-1549538