[lldb/win] Default to native PDB reader when building with LLVM_ENABLE_DIA_SDK=NO

[thakis]

Summary

Trying to use the DIA SDK reader only to fail with "DIA SDK wasn't enabled"
isn't very useful. The native PDB reader is missing some stuff, but it's
still better than nothing.

Reduces number of lldb-check-shell test failures with LLVM_ENABLE_DIA_SDK=NO from
27 to 15.

[thakis]

slightly simpler preprocessor goop

[thakis]

slightly nicer preprocessor goop in more correct

[amccarth]

LGTM

[labath]

lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp

89–91

What's the value of LLVM_ENABLE_DIA_SDK on non-windows platforms? It seems to be zero on my (linux) system. Could this be just #if LLVM_ENABLE_DIA_SDK ?

[MehdiChinoune]

This commit make building standalone LLDB impossible on Windows. llvm/Config/config.h file is only generated at build-time and not get installed with llvm.
Please Fix it.

lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp

 #include "llvm/DebugInfo/PDB/PDBSymbolTypeEnum.h"
 #include "llvm/DebugInfo/PDB/PDBSymbolTypeTypedef.h"
 #include "llvm/DebugInfo/PDB/PDBSymbolTypeUDT.h"
 
 #include "Plugins/Language/CPlusPlus/CPlusPlusLanguage.h"
 #include "Plugins/Language/CPlusPlus/MSVCUndecoratedNameParser.h"
 #include "Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.h"
 
+#if defined(_WIN32)
+#include "llvm/Config/config.h"
+#endif
+
 using namespace lldb;
 using namespace lldb_private;
 using namespace llvm::pdb;
 
 LLDB_PLUGIN_DEFINE(SymbolFilePDB)
 
 char SymbolFilePDB::ID;
 

 bool ShouldAddLine(uint32_t requested_line, uint32_t actual_line,
                    uint32_t addr_length) {
   return ((requested_line == 0 || actual_line == requested_line) &&
           addr_length > 0);
 }
 } // namespace
 
 static bool ShouldUseNativeReader() {
 #if defined(_WIN32)
+#if LLVM_ENABLE_DIA_SDK
   llvm::StringRef use_native = ::getenv("LLDB_USE_NATIVE_PDB_READER");
-  return use_native.equals_insensitive("on") ||
-         use_native.equals_insensitive("yes") ||
-         use_native.equals_insensitive("1") ||
-         use_native.equals_insensitive("true");
-#else
-  return true;
+  if (use_native.equals_insensitive("on") ||
+      use_native.equals_insensitive("true"))
+    return false;
+#endif
 #endif
+  return true;
 }
 
 void SymbolFilePDB::Initialize() {
   if (ShouldUseNativeReader()) {
     npdb::SymbolFileNativePDB::Initialize();
   } else {
     PluginManager::RegisterPlugin(GetPluginNameStatic(),
                                   GetPluginDescriptionStatic(), CreateInstance,