gcc-lld mvp

ignore test if rust-lld not found

create ld -> rust-lld symlink at build time instead of run time

for testing in ci

copy instead of symlinking

remove linux check

test for linker, suggestions from bjorn3

fix overly restrictive lld matcher

use -Zgcc-ld flag instead of -Clinker-flavor

refactor code adding lld to gcc path

revert ci changes

suggestions from petrochenkov

rename gcc_ld to gcc-ld in dirs

compiler/rustc_session/src/config.rs

@@ -2417,6 +2417,7 @@ impl PpMode {
 /// we have an opt-in scheme here, so one is hopefully forced to think about
 /// how the hash should be calculated when adding a new command-line argument.
 crate mod dep_tracking {
+    use super::LdImpl;
     use super::{
         CFGuard, CrateType, DebugInfo, ErrorOutputType, InstrumentCoverage, LinkerPluginLto,
         LtoCli, OptLevel, OutputTypes, Passes, SourceFileHashAlgorithm, SwitchWithOptPath,
@@ -2497,6 +2498,7 @@ crate mod dep_tracking {
         SymbolManglingVersion,
         SourceFileHashAlgorithm,
         TrimmedDefPaths,
+        Option<LdImpl>,
     );
 
     impl<T1, T2> DepTrackingHash for (T1, T2)