[CUDA] Emit a warning if a CUDA host/device/global attribute is placed after '(...)'.

Summary:
This is probably the sane place for the attribute to go, but nvcc
specifically rejects it.  Other GNU-style attributes are allowed in this
position (although judging from the warning it emits for
host/device/global, those attributes are applied to the lambda's
anonymous struct, not to the function itself).

It would be nice to have a FixIt message here, but doing so, or even
just getting the correct range for the attribute, including its '((' and
'))'s, is apparently Hard.

Reviewers: rnk

Subscribers: cfe-commits, tra

Differential Revision: https://reviews.llvm.org/D25115

llvm-svn: 282911