[DWARFLinkerParallel] change thread_local to LLVM_THREAD_LOCAL for StringPool.

[avl]

Summary

Not all platforms support C++11 thread_local. Use portable
LLVM_THREAD_LOCAL macro instead.

[avl]

close in favor D147649

llvm/include/llvm/DWARFLinkerParallel/StringPool.h

 /// and a string body which is placed right after StringEntry.
 using StringEntry = StringMapEntry<DwarfStringPoolEntry *>;
 
 class PerThreadStringAllocator
     : public AllocatorBase<PerThreadStringAllocator> {
 public:
   inline LLVM_ATTRIBUTE_RETURNS_NONNULL void *Allocate(size_t Size,
                                                        size_t Alignment) {
-    return ThreadLocalAllocator.Allocate(Size, Align(Alignment));
+    return getAllocatorPtr()->Allocate(Size, Align(Alignment));
   }
 
   // Pull in base class overloads.
   using AllocatorBase<PerThreadStringAllocator>::Allocate;
 
 private:
-  static thread_local BumpPtrAllocator ThreadLocalAllocator;
+  BumpPtrAllocator *getAllocatorPtr() {
+    if (ThreadLocalAllocator == nullptr)
+      ThreadLocalAllocator = new BumpPtrAllocator();
+
+    return ThreadLocalAllocator;
+  }
+
+  static LLVM_THREAD_LOCAL BumpPtrAllocator *ThreadLocalAllocator;
 };
 
 class StringPoolEntryInfo {
 public:
   /// \returns Hash value for the specified \p Key.
   static inline uint64_t getHashValue(const StringRef &Key) {
     return xxHash64(Key);
   }

llvm/lib/DWARFLinkerParallel/StringPool.cpp

 //=== StringPool.cpp ------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/DWARFLinkerParallel/StringPool.h"
 
-thread_local llvm::BumpPtrAllocator
-    llvm::dwarflinker_parallel::PerThreadStringAllocator::ThreadLocalAllocator;
+LLVM_THREAD_LOCAL llvm::BumpPtrAllocator
+    *llvm::dwarflinker_parallel::PerThreadStringAllocator::ThreadLocalAllocator;