Auto merge of #147022 - Zalathar:no-args, r=wesleywiser

Remove current code for embedding command-line args in PDB

The compiler currently has code that will obtain a list of quoted command-line arguments, and pass it through to TargetMachine creation, so that the command-line args can be embedded in PDB output.

This PR removes that code, due to subtle concerns that might not have been apparent when it was originally added.

---

Those concerns include:
- The entire command-line quoting process is repeated every time a target-machine-factory is created. In incremental builds this typically occurs 500+ times, instead of happening only once. The repeated quoting constitutes a large chunk of instructions executed in the `large-workspace` benchmark.
  - See https://github.com/rust-lang/rust/pull/146804#issuecomment-3317322958 for an example of the perf consequences of skipping all that work.
  - This overhead occurs even when building for targets or configurations that don't emit PDB output.
- Command-line arguments are obtained in a way that completely bypasses the query system, which is a problem for the integrity of incremental compilation.
  - Fixing this alone is likely to inhibit incremental rebuilds for most or all CGUs, even in builds that don't emit PDB output.
- Command-line arguments and the executable path are obtained in a way that completely bypasses the compiler's path-remapping system, which is a reproducibility hazard.
  - https://github.com/rust-lang/rust/issues/128842

---

Relevant PRs:
- https://github.com/rust-lang/rust/pull/113492
- https://github.com/rust-lang/rust/pull/130446
- https://github.com/rust-lang/rust/pull/131805
- https://github.com/rust-lang/rust/pull/146700
- https://github.com/rust-lang/rust/pull/146973

Zulip thread:
- https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/Some.20PDB.20info.20bypasses.20the.20query.20system.20and.20path.20remapping/with/541432211

---

According to rust-lang/rust#96475, one of the big motivations for embedding the command-line arguments was to enable tools like Live++. [It appears that Live++ doesn't actually support Rust yet](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/embeded.20compiler.20args.20and.20--remap-path-prefix/near/523800010), so it's possible that there aren't any existing workflows for this removal to break.

In the future, there could be a case for reintroducing some or all of this functionality, guarded behind an opt-in flag so that it doesn't cause problems for other users. But as it stands, the current implementation puts a disproportionate burden on other users and on compiler maintainers.

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2330,10 +2330,6 @@ unsafe extern "C" {
         OutputObjFile: *const c_char,
         DebugInfoCompression: *const c_char,
         UseEmulatedTls: bool,
-        Argv0: *const c_uchar, // See "PTR_LEN_STR".
-        Argv0Len: size_t,
-        CommandLineArgs: *const c_uchar, // See "PTR_LEN_STR".
-        CommandLineArgsLen: size_t,
         UseWasmEH: bool,
     ) -> *mut TargetMachine;