[CUDA] Do not allow non-empty destructors for global device-side variables.
According to Cuda Programming guide (v7.5, E2.3.1):
device, constant and shared variables defined in namespace
scope, that are of class type, cannot have a non-empty constructor or a
Clang already deals with device-side constructors (see D15305).
This patch enforces similar rules for destructors.
Differential Revision: http://reviews.llvm.org/D20140