[clang] [Serialization] Fix lazy template loading (PR #133057)

[Jonas Hahnfeld via cfe-commits]

hahnjo wrote:

> The simplified script: https://pastebin.com/udVTaPYV

Aaaah, the important line is `EXTRA_CFLAGS='-Xclang -fallow-pcm-with-compiler-errors -ferror-limit=0'`. With that I indeed get the following diff between logs from `main` and a rebased version of this branch:
```diff
--- main.log    2025-04-11 14:31:26.655249634 +0200
+++ clang-modules-rebased.log   2025-04-11 14:30:12.184305904 +0200
@@ -417,12 +417,15 @@
 TR7.cc:4:1: error: a type specifier is required for all declarations
     4 | std (
       | ^
-TR7.cc:8:1: error: 'operator type-parameter-0-0' is a private member of 'sr::g<char, sr::kh, wjr>'
+TR7.cc:7:3: error: use of overloaded operator '=' is ambiguous (with operand types 'uz<wd>' and 'g<char, kh, wjr>')
+    7 | q =
+      | ~ ^
     8 | dp(h, '\n')
-      | ^~~~~~~~~~~
-./UL8.h:6:1: note: implicitly declared private here
-    6 | operator pzx(;
-      | ^
+      | ~~~~~~~~~~~
+L3Z:31:7: note: candidate function (the implicit copy assignment operator)
+   31 | class uz {typede x t;
+      |       ^
+L3Z:31:7: note: candidate function (the implicit move assignment operator)
 TR7.cc:8:12: error: expected ';' after expression
     8 | dp(h, '\n')
       |            ^
```

When I have time, I will need to see that I turn the reduced example into actual valid code to understand what is going on...

https://github.com/llvm/llvm-project/pull/133057