[llvm] statically link TableGenTests (#147577)
## Purpose
Statically link `TableGenTests` so it can still build when linked
against an LLVM Windows DLL.
## Background
The effort to build LLVM as a WIndows DLL is tracked in #109483.
Additional context is provided in [this
discourse](https://discourse.llvm.org/t/psa-annotating-llvm-public-interface/85307).
If `TableGenTests` is linked against LLVM built as a DLL on Windows, it
will fail due to a large number of duplicate symbols found in both the
LLVM DLL and TableGen libraries. This is because `LLVMTableGenBasic` and
`LLVMTableGenCommon` are linked statically against LLVM (using
`DISABLE_LLVM_LINK_LLVM_DYLIB`) so already contain a sub-set of symbols
also exported from the LLVM DLL.
This patch was originally part of #145448.
