[lld] [llvm] [clang] Embed the command line arguments during LTO (PR #79390)

[Mircea Trofin via cfe-commits]

mtrofin wrote:

> > I haven't checked closely yet, but it seems like you need to add tests.
> 
> Could you provide some guidance on what kind of tests to add and how to actually run them locally? First I wanted to get the builtkite job to be green, but it seems to be failing on some unrelated test where LLD cannot be found...


You'd want to add tests under `lld/test[COFF|ELF|MachO|MinGW|wasm]`

To run tests locally - assuming you're in the root of the repo:

```
mkdir build
cmake -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_ENABLE_ASSERTIONS=ON ../llvm
ninja check-all
```

Main pieces there are:
* the list under LLVM_ENABLE_PROJECTS - you want to make sure regression tests for thinlto + embed bitcode pass (e.g. `clang/test/CodeGen/thinlto_embed_bitcode.ll`), and those are under clang; and lld is self-explanatory.
* `ninja check-all`

More info [here](https://llvm.org/docs/GettingStarted.html#getting-the-source-code-and-building-llvm)

https://github.com/llvm/llvm-project/pull/79390