[NFC][AArch64] Get extension strings directly from ArchInfo in target parser

clang/lib/Basic/Targets/AArch64.cpp

if ((Feature[0] == '?' || Feature[0] == '+')) {
       if (AArch64TargetInfo::getFeatureDepOptions(Feature.substr(1), Options)) {
         SmallVector<StringRef, 1> AttrFeatures;
         StringRef(Options).split(AttrFeatures, ",");
         for (auto F : AttrFeatures)
           UpdatedFeaturesVec.push_back(F.str());
       }
     }
   for (const auto &Feature : FeaturesVec)
+    if (Feature[0] != '?') {
+      std::string UpdatedFeature = Feature;
       if (Feature[0] == '+') {
-      std::string F;
-      llvm::AArch64::getFeatureOption(Feature, F);
-      UpdatedFeaturesVec.push_back(F);
-    } else if (Feature[0] != '?')
-      UpdatedFeaturesVec.push_back(Feature);
+        std::optional<llvm::AArch64::ExtensionInfo> Extension =
+          llvm::AArch64::parseArchExtension(Feature.substr(1));
+        if (Extension)
+          UpdatedFeature = Extension->Feature.str();
+      }
+      UpdatedFeaturesVec.push_back(UpdatedFeature);
+    }
 
   return TargetInfo::initFeatureMap(Features, Diags, CPU, UpdatedFeaturesVec);
 }
 
 // Parse AArch64 Target attributes, which are a comma separated list of:
 //  "arch=<arch>" - parsed to features as per -march=..
 //  "cpu=<cpu>" - parsed to features as per -mcpu=.., with CPU set to <cpu>
 //  "tune=<cpu>" - TuneCPU set to <cpu>

llvm/include/llvm/TargetParser/AArch64TargetParser.h

 
 bool getExtensionFeatures(uint64_t Extensions,
                           std::vector<StringRef> &Features);
 
 StringRef getArchExtFeature(StringRef ArchExt);
 StringRef resolveCPUAlias(StringRef CPU);
 
 // Information by Name
-void getFeatureOption(StringRef Name, std::string &Feature);
 std::optional<ArchInfo> getArchForCpu(StringRef CPU);
 
 // Parser
 std::optional<ArchInfo> parseArch(StringRef Arch);
 std::optional<ExtensionInfo> parseArchExtension(StringRef Extension);
 // Given the name of a CPU or alias, return the correponding CpuInfo.
 std::optional<CpuInfo> parseCpu(StringRef Name);
 // Used by target parser tests

llvm/lib/TargetParser/AArch64TargetParser.cpp

 using namespace llvm;
 
 static unsigned checkArchVersion(llvm::StringRef Arch) {
   if (Arch.size() >= 2 && Arch[0] == 'v' && std::isdigit(Arch[1]))
     return (Arch[1] - 48);
   return 0;
 }
 
-void AArch64::getFeatureOption(StringRef Name, std::string &Feature) {
-  for (const auto &E : llvm::AArch64::Extensions) {
-    if (Name == E.Name) {
-      Feature = E.Feature;
-      return;
-    }
-  }
-  Feature = Name.str();
-}
-
 std::optional<AArch64::ArchInfo> AArch64::getArchForCpu(StringRef CPU) {
   if (CPU == "generic")
     return ARMV8A;
 
   // Note: this now takes cpu aliases into account
   std::optional<CpuInfo> Cpu = parseCpu(CPU);
   if (!Cpu)
     return {};