[Legacy ThinLTO] NFC: Use explicit static; shrink anonymous namespace

Improve compliance with
https://llvm.org/docs/CodingStandards.html#anonymous-namespaces:
> [Only] use [anonymous namespaces] for class declarations.

Author: hubert-reinterpretcast

llvm/lib/LTO/ThinLTOCodeGenerator.cpp

@@ -85,8 +85,6 @@ extern cl::opt<std::optional<uint64_t>, false, remarks::HotnessThresholdParser>
 extern cl::opt<std::string> RemarksFormat;
 }
 
-namespace {
-
 // Default to using all available threads in the system, but using only one
 // thred per core, as indicated by the usage of
 // heavyweight_hardware_concurrency() below.
@@ -326,8 +324,8 @@ computeGUIDPreservedSymbols(const lto::InputFile &File,
   return GUIDPreservedSymbols;
 }
 
-std::unique_ptr<MemoryBuffer> codegenModule(Module &TheModule,
-                                            TargetMachine &TM) {
+static std::unique_ptr<MemoryBuffer> codegenModule(Module &TheModule,
+                                                   TargetMachine &TM) {
   SmallVector<char, 128> OutputBuffer;
 
   // CodeGen
@@ -347,6 +345,7 @@ std::unique_ptr<MemoryBuffer> codegenModule(Module &TheModule,
       std::move(OutputBuffer), /*RequiresNullTerminator=*/false);
 }
 
+namespace {
 /// Manage caching for a single Module.
 class ModuleCacheEntry {
   SmallString<128> EntryPath;
@@ -424,6 +423,7 @@ class ModuleCacheEntry {
                                        toString(std::move(Err)).c_str()));
   }
 };
+} // end anonymous namespace
 
 static std::unique_ptr<MemoryBuffer>
 ProcessThinLTOModule(Module &TheModule, ModuleSummaryIndex &Index,
@@ -541,8 +541,6 @@ static void initTMBuilder(TargetMachineBuilder &TMBuilder,
   TMBuilder.TheTriple = std::move(TheTriple);
 }
 
-} // end anonymous namespace
-
 void ThinLTOCodeGenerator::addModule(StringRef Identifier, StringRef Data) {
   MemoryBufferRef Buffer(Data, Identifier);