[llvm] [MC][NFC] Store SubTypeKV names as string table (PR #207580)

[Fangrui Song via llvm-commits]

================
@@ -125,7 +124,7 @@ static void Help(ArrayRef<StringRef> CPUNames,
 
   // Print the CPU table.
   errs() << "Available CPUs for this target:\n\n";
-  for (auto &CPUName : CPUNames) {
+  for (auto &CPUName : drop_begin(CPUNames)) {
----------------
MaskRay wrote:

I wonder whether we should change the `StringTable` iterator to skip the initial '\0' element (#123302), otherwise most use cases would probably need `drop_begin`.

https://github.com/llvm/llvm-project/pull/207580