Mechanically port bulk of x86 builtins to TableGen

The goal is to make incremental (if small) progress towards fully
TableGen'ed builtins, and to unblock #120534 by gaining access to more
powerful TableGen-based representations.

The bulk `.td` file addition was generated with the help of a very rough
Python script. That script made no attempt to be robust or reusable, it
specifically handled only the cases in the X86 `.def` file.

Four entries from the `.def` file were not handled automatically as they
used `BUILTIN` rather than `TARGET_BUILTIN`. These were ported by hand
to an empty-feature `TargetBuiltin` entry, which seems like a better
match.

For all the automatically ported entries, the results were compared by
sorting and diffing the `.def` file and the generated `.inc` file. The
only differences were:

- Different horizontal whitespace

- Additional entries that had already been ported to the `.td` file.

- Systematically using `Oi` instead of `LLi` for the type `long long
  int`. The `.def` file uses a mixture of `Oi` and `LLi`. I chose the
  shorter encoding.

This gives me high confidence in the correctness of the change.

Author: chandlerc

clang/include/clang/Basic/BuiltinsBase.td

@@ -95,9 +95,6 @@ class CustomEntry {
 }
 
 class AtomicBuiltin : Builtin;
-class TargetBuiltin : Builtin {
-  string Features = "";
-}
 
 class LibBuiltin<string header, string languages = "ALL_LANGUAGES"> : Builtin {
   string Header = header;
@@ -122,6 +119,14 @@ class OCL_DSELangBuiltin : LangBuiltin<"OCL_DSE">;
 class OCL_GASLangBuiltin : LangBuiltin<"OCL_GAS">;
 class OCLLangBuiltin : LangBuiltin<"ALL_OCL_LANGUAGES">;
 
+class TargetBuiltin : Builtin {
+  string Features = "";
+}
+class TargetLibBuiltin : TargetBuiltin {
+  string Header;
+  string Languages = "ALL_LANGUAGES";
+}
+
 class Template<list<string> substitutions,
                list<string> affixes,
                bit as_prefix = 0> {