[clang] [Driver] Add ExclusiveGroup feature to multilib.yaml. (PR #69447)

[Fangrui Song via cfe-commits]

================
@@ -96,13 +98,36 @@ bool MultilibSet::select(const Multilib::flags_list &Flags,
                          llvm::SmallVector<Multilib> &Selected) const {
   llvm::StringSet<> FlagSet(expandFlags(Flags));
   Selected.clear();
-  llvm::copy_if(Multilibs, std::back_inserter(Selected),
-                [&FlagSet](const Multilib &M) {
-                  for (const std::string &F : M.flags())
-                    if (!FlagSet.contains(F))
-                      return false;
-                  return true;
-                });
+
+  // Decide which multilibs we're going to select at all.
+  llvm::DenseSet<StringRef> ExclusiveGroupsSelected;
+
----------------
MaskRay wrote:

The common llvm-project style does not typically insert a blank line after a variable declaration, different from the Linux kernel style.

https://github.com/llvm/llvm-project/pull/69447