[CMake] Fix recompile all .inc files with LLVM_OPTIMIZED_TABLEGEN in Visual Studio.

After some moment VS solution generated with LLVM_OPTIMIZED_TABLEGEN started to
generate all .inc files for each build. The reason was it had
"<path to native tablegen>/llvm-tblgen" without .exe as a dependency.

Differential Revision: https://reviews.llvm.org/D107898