Auto merge of #75956 - jonas-schievink:lto-opt-sz, r=tmiasko

Fix -Clinker-plugin-lto with opt-levels s and z

Pass s and z as `-plugin-opt=O2` to the linker. This is what `-Os` and `-Oz` correspond to, apparently.

Fixes https://github.com/rust-lang/rust/issues/75940

src/test/ui/lto-opt-level-s.rs

@@ -0,0 +1,7 @@
+// compile-flags: -Clinker-plugin-lto -Copt-level=s
+// build-pass
+// no-prefer-dynamic
+
+#![crate_type = "rlib"]
+
+pub fn foo() {}

src/test/ui/lto-opt-level-z.rs

@@ -0,0 +1,7 @@
+// compile-flags: -Clinker-plugin-lto -Copt-level=z
+// build-pass
+// no-prefer-dynamic
+
+#![crate_type = "rlib"]
+
+pub fn foo() {}