[clang] [clang-tools-extra] [Clang] Add a builtin that deduplicate types into a pack (PR #106730)

[Kazu Hirata via cfe-commits]

kazutakahirata wrote:

@ilya-biryukov After this PR, I'm getting:

```
lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp:4148:11: error: enumeration value 'SubstBuiltinTemplatePack' not handled in switch [-Werror,-Wswitch]
 4148 |   switch (qual_type->getTypeClass()) {
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~
lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp:4852:11: error: enumeration value 'SubstBuiltinTemplatePack' not handled in switch [-Werror,-Wswitch]
 4852 |   switch (qual_type->getTypeClass()) {
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~
lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp:5153:11: error: enumeration value 'SubstBuiltinTemplatePack' not handled in switch [-Werror,-Wswitch]
 5153 |   switch (qual_type->getTypeClass()) {
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~
3 errors generated.
```

Is there any way you could take look?


https://github.com/llvm/llvm-project/pull/106730