[llvm] [LLVM][MC] Add support to cull inactive decoders in decoder emitter (PR #154865)

[Rahul Joshi via llvm-commits]

================
@@ -1158,6 +1158,13 @@ class InstrInfo {
   //
   // This option is a temporary migration help. It will go away.
   bit guessInstructionProperties = true;
+
+  // Generate decoders that are specialized per bit width in the generated
+  // decoder/disassembler. This requires use of different `InsnType` for
+  // different bitwidths and defining `InsnBitWidth` template specialization for
+  // the `InsnType` types used. Some common specializations are already defined
+  // in MCDecoder.h.
+  bit SpecializeDecodersPerBitwidth = false;
----------------
jurahul wrote:

We did not. Based on previous experience with `LargeTable`, the option in InstrInfo is slightly more convenient as we don't need to modify the makefile, which is a +ve. Else we need to update the CMake and bazel makefiles both and any additional build systems files that may be used downstream.

https://github.com/llvm/llvm-project/pull/154865