linker: also pass debuginfo compression flags

We support compressing debuginfo during codegen, but until this patch we
didn't pass the flag to the linker. Doing so means we'll respect the
requested compression even when building binaries or dylibs. This
produces much smaller binaries: in my testing a debug build of ripgrep
goes from 85M to 32M, and the target/ directory (after a clean build in
both cases) goes from 508M to 329M just by enabling zlib compression of
debuginfo.

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -626,6 +626,15 @@ impl<'a> Linker for GccLinker<'a> {
                 self.linker_arg("--strip-all");
             }
         }
+        match self.sess.opts.unstable_opts.debuginfo_compression {
+            config::DebugInfoCompression::None => {}
+            config::DebugInfoCompression::Zlib => {
+                self.linker_arg("--compress-debug-sections=zlib");
+            }
+            config::DebugInfoCompression::Zstd => {
+                self.linker_arg("--compress-debug-sections=zstd");
+            }
+        }
     }
 
     fn no_crt_objects(&mut self) {