[DWARFLinker] Avoid repeated hash lookups (NFC) (#108737)

Author: kazutakahirata

llvm/lib/DWARFLinker/Parallel/OutputSections.h

@@ -371,16 +371,11 @@ class OutputSections {
   /// If descriptor does not exist then creates it.
   SectionDescriptor &
   getOrCreateSectionDescriptor(DebugSectionKind SectionKind) {
-    SectionsSetTy::iterator It = SectionDescriptors.find(SectionKind);
-
-    if (It == SectionDescriptors.end()) {
-      SectionDescriptor *Section =
-          new SectionDescriptor(SectionKind, GlobalData, Format, Endianness);
-      auto Result = SectionDescriptors.try_emplace(SectionKind, Section);
-      assert(Result.second);
+    auto [It, Inserted] = SectionDescriptors.try_emplace(SectionKind);
 
-      It = Result.first;
-    }
+    if (Inserted)
+      It->second = std::make_shared<SectionDescriptor>(SectionKind, GlobalData,
+                                                       Format, Endianness);
 
     return *It->second;
   }