[lldb] Silence warning with latest MSVC

Fixes several of these:
```
[3370/3822] Building CXX object tools\lldb\source\Plugins\Process\U...lldbPluginProcessUtility.dir\NativeRegisterContextDBReg_x86.cpp.ob
C:\git\llvm-project\lldb\source\Plugins\Process\Utility\NativeRegisterContextDBReg_x86.h(23): warning C4589: Constructor of abstract class 'lldb_private::NativeRegisterContextDBReg_x86' ignores initializer for virtual base class 'lldb_private::NativeRegisterContextRegisterInfo'
C:\git\llvm-project\lldb\source\Plugins\Process\Utility\NativeRegisterContextDBReg_x86.h(23): note: virtual base classes are only initialized by the most-derived type
```

Author: aganea

lldb/cmake/modules/LLDBConfig.cmake

@@ -215,6 +215,7 @@ if( MSVC )
     -wd4251 # Suppress 'warning C4251: T must have dll-interface to be used by clients of class U.'
     -wd4521 # Suppress 'warning C4521: 'type' : multiple copy constructors specified'
     -wd4530 # Suppress 'warning C4530: C++ exception handler used, but unwind semantics are not enabled.'
+    -wd4589 # Suppress 'warning C4589: Constructor of abstract class 'lldb_private::NativeRegisterContextDBReg_x86' ignores initializer for virtual base class 'lldb_private::NativeRegisterContextRegisterInfo''
   )
 endif()