[ManagedStatic] Fix build errors with clang-tblgen in Debug mode using MSVC 2019 v16.6

After updating MSVS19 from v16.4 to v16.6 I faced with a build errors compiling in Debug mode.
It complains on clang-tblgen.exe and llvm-tblgen.exe cmd line args.
VS compiler had a bug. It dynamically creates an object with constexpr ctor in Debug mode. This bug was fixed in VS2019 v16.5.
A workaround was implemented for that and everything works until v16.5 comes.
The workaround became irrelevant since v16.5 and caused build errors.
So I disabled the workaround for VS2019 v16.5 and higher.

This relates to http://llvm.org/PR41367.

Differential Revision: https://reviews.llvm.org/D80433