Started implementing variable templates. Top level declarations should be fully supported, up to some limitations documented as FIXMEs or TODO. Static data member templates work very partially. Static data member templates of class templates need particular attention...

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187762 91177308-0d34-0410-b5e6-96231b3b80d8