[clang] [Sema] Substitute parameter packs when deduced from function arguments (PR #79371)

[Gábor Spaits via cfe-commits]

spaits wrote:

Thank you for reviewing.

Before merge we should take a look at the CI.

It still fails for libc++ 26 suite, with the same reason as before.

I wanted to reproduce the issue. I built libc++ with the clang++ I compiled:
```
cmake -S "../runtimes" -GNinja \
          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
          -DLIBCXX_CXX_ABI=libcxxabi \
          -DCMAKE_BUILD_TYPE=Debug \
          -DLIBCXX_TEST_PARAMS="std=c++26" \
          -DLIBCXXABI_TEST_PARAMS="std=c++26" \
          -DCMAKE_CXX_COMPILER=/home/spaits/repo/llvm-project/build/bin/clang++ \
          -DLLVM_DIR=/home/spaits/repo/llvm-project/build/lib/cmake/llvm
```
Then I run the test:
```
 /home/spaits/repo/llvm-project/build/bin/llvm-lit -a /home/spaits/repo/llvm-project/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp
```

Everything worked fine for me.
I don't know why the CI always fails for my PR with the same reason. It looks like an env issue in the CI, but it can not be that since other PRs are getting green runs.

https://github.com/llvm/llvm-project/pull/79371