[TargetParser] Avoid repeated hash lookups (NFC) (#131555)

Author: kazutakahirata

llvm/lib/TargetParser/RISCVISAInfo.cpp

@@ -839,10 +839,11 @@ void RISCVISAInfo::updateImplication() {
     std::for_each(Range.first, Range.second,
                   [&](const ImpliedExtsEntry &Implied) {
                     const char *ImpliedExt = Implied.ImpliedExt;
-                    if (Exts.count(ImpliedExt))
+                    auto [It, Inserted] = Exts.try_emplace(ImpliedExt);
+                    if (!Inserted)
                       return;
                     auto Version = findDefaultVersion(ImpliedExt);
-                    Exts[ImpliedExt] = *Version;
+                    It->second = *Version;
                     WorkList.push_back(ImpliedExt);
                   });
   }