linker: Remove -Zgcc-ld option

[petrochenkov]

It is subsumed by -Clinker-flavor=*-lld-cc -Clink-self-contained=+linker options now.

r? @lqd

[lqd]

r=me with the 2 nits fixed.

As well as:

• I don't believe we use the enum anymore and can also remove

  rust/compiler/rustc_session/src/options.rs

  Lines 1910 to 1913 in 7ca090f

  	#[derive(Clone, Copy, Hash)]
  	pub enum LdImpl {
  	Lld,
  	}

• and in turn of course remove

  rust/compiler/rustc_session/src/config.rs

  Line 3277 in 7ca090f

  Option<LdImpl>,

  and the LdImpl import

[lqd]

(GH UI doing a poor job at showing review comments without duplicates ...)

[petrochenkov]

@bors r=lqd

[bors]

📌 Commit b563595 has been approved by lqd

It is now in the queue for this repository.

[bors]

⌛ Testing commit b563595 with merge ab039f7...

[bors]

☀️ Test successful - checks-actions
Approved by: lqd
Pushing ab039f7 to master...

[rust-timer]

Finished benchmarking commit (ab039f7): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	2
All ❌✅ (primary)	-	-	0

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 624.124s -> 621.59s (-0.41%)
Artifact size: 270.68 MiB -> 270.70 MiB (0.01%)

[AlexTMjugador]

Was this unstable option really subsumed by the -Clinker-flavor=*-lld-cc -Clink-self-contained=+linker flags, though?

The combination of -Clinker=aarch64-linux-gnu-gcc -Clinker-flavor=gnu-lld-cc does not seem to work today (rustc 1.76.0-nightly (503e12932 2023-12-07)) to use a cross-compiling linker with LLD, and previously -Zgcc-ld=lld was a way to tackle rust-lang/rustup#3324 (see also #89626 (comment)).

Edit: it appears my issue is a bit more complex than it looks at a first glance (I'm debugging recent CI build issues at https://github.com/OptiVorbis/OptiVorbis/actions/runs/7120629253/job/19388265619). When using these flags through cargo build, the linker invocation as shown by --print link-args looks fine. But the same flags under cargo test cause the system cc linker to be used instead. Maybe this is related to using Cargo's -Zdoctest-xcompile? In any case, I don't think this is related to this change after some investigation.