[PSV] Update API to be able to use TargetCustom without UB.

getTargetCustom() requires values for "Kind" in the constructor
that are not in the PSVKind enum. Passing a value that is not inside
an enum as an argument to a constructor of the type of the enum is
UB. Changing to the underlying type of the enum would solve the UB

Differential Revision: https://reviews.llvm.org/D50909

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340200 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed