[LLVM][CodingStandard] Extend namespace qualifier rule to variables/classes

[jurahul]

Extend CS rule to use namespace qualifiers to define previously declared functions to variables and classes as well.

[dwblaikie]

I think we might as well generalize this over all declarations, rather than specifying only functions and variables (we shouldn't have many variables declared in headers anyway, but similarly, might have a small number of opaque classes declared in headers too)

[jurahul]

Note that this specific section is not about requiring declarations in headers but about using namespace qualifiers in definitions. Are you suggesting that it can be used/should be used for opaque classes like RecordKeeperImpl in TableGen? I just tested it out and it works, so yeah, I can extend the example to cover opaque classes that are declared in LLVM namespace in a header but defined in .cpp files.

[jurahul]

Done, added example of an opaque class and changed the language to be more general.

[jurahul]

Thanks, I'll wait for other folks to chime in as well before merging.

[jh7370]

Seems reasonable to me.

[jurahul]

@nikic will wait for you approval as well before merging.

[nikic]

LGTM