[clang] Fix Strong VTables Accidentally Emitted by #159856 (PR #200942)

[Patrick Simmons via cfe-commits]

linuxrocks123 wrote:

> Regression tests should be reduced to just the relevant constructs; please don't include a copy of the entire C++ standard library.
> 
> Please fix GetAddrOfVTable() so it computes the correct linkage in the first place; trying to fix the linkage later is confusing at best.

@efriedma-quic the function which computes the linkage is `CodeGenModule::getVTableLinkage`.  This function is being called before it's supposed to be called, hence the problem.  I would not feel good about changing `CodeGenModule::getVTableLinkage` instead because changes to that code would affect code generation for all targets, not just OpenMP offload.

https://github.com/llvm/llvm-project/pull/200942