[StrTable] Add factored prefix for Hexagon

This target's builtins have an especially long prefix and so we get over
2x reduction in string table size required with this change.

Author: chandlerc

clang/include/clang/Basic/BuiltinsHexagon.td

@@ -56,10 +56,13 @@ def HVXV65 : HVXV<"65", HVXV66>;
 def HVXV62 : HVXV<"62", HVXV65>;
 def HVXV60 : HVXV<"60", HVXV62>;
 
+def HexagonPrefix : NamePrefix<"__builtin_HEXAGON_">;
+
 class HexagonBuiltin<string prototype> : TargetBuiltin {
-  let Spellings = ["__builtin_HEXAGON_" # NAME];
+  let Spellings = [NAME];
   let Prototype = prototype;
   let Features = V5.Features;
+  let RequiredNamePrefix = HexagonPrefix; // Adds a prefix to the name.
 }
 
 class HexagonBuiltinNoPrefix<string prototype> : TargetBuiltin {

clang/lib/Basic/Targets/Hexagon.cpp

@@ -216,7 +216,14 @@ static constexpr Builtin::Info BuiltinInfos[] = {
 #include "clang/Basic/BuiltinsHexagon.inc"
 #undef GET_BUILTIN_INFOS
 };
-static_assert(std::size(BuiltinInfos) == NumBuiltins);
+
+static constexpr Builtin::Info PrefixedBuiltinInfos[] = {
+#define GET_BUILTIN_PREFIXED_INFOS
+#include "clang/Basic/BuiltinsHexagon.inc"
+#undef GET_BUILTIN_PREFIXED_INFOS
+};
+static_assert((std::size(BuiltinInfos) + std::size(PrefixedBuiltinInfos)) ==
+              NumBuiltins);
 
 bool HexagonTargetInfo::hasFeature(StringRef Feature) const {
   std::string VS = "hvxv" + HVXVersion;
@@ -277,5 +284,6 @@ void HexagonTargetInfo::fillValidCPUList(
 
 llvm::SmallVector<Builtin::InfosShard>
 HexagonTargetInfo::getTargetBuiltins() const {
-  return {{&BuiltinStrings, BuiltinInfos}};
+  return {{&BuiltinStrings, BuiltinInfos},
+          {&BuiltinStrings, PrefixedBuiltinInfos, "__builtin_HEXAGON_"}};
 }