[llvm] Fix comment nits in Module class, NFC.

[XiaodongLoong]

Summary

There is no member called "GlobalValRefMap" in Module class.
It has been changed to "GlobalList".

[efriedma]

LGTM

llvm/include/llvm/IR/Module.h

 
 /// A Module instance is used to store all the information related to an
 /// LLVM module. Modules are the top level container of all other LLVM
 /// Intermediate Representation (IR) objects. Each module directly contains a
 /// list of globals variables, a list of functions, a list of libraries (or
 /// other modules) this module depends on, a symbol table, and various data
 /// about the target's characteristics.
 ///
-/// A module maintains a GlobalValRefMap object that is used to hold all
+/// A module maintains a GlobalList object that is used to hold all
 /// constant references to global variables in the module.  When a global
-/// variable is destroyed, it should have no entries in the GlobalValueRefMap.
+/// variable is destroyed, it should have no entries in the GlobalList.
 /// The main container class for the LLVM Intermediate Representation.
 class LLVM_EXTERNAL_VISIBILITY Module {
   /// @name Types And Enumerations
   /// @{
 public:
   /// The type for the list of global variables.
   using GlobalListType = SymbolTableList<GlobalVariable>;
   /// The type for the list of functions.