Workaround rust-lang/rust#108166

Author: bjorn3

build_system/build_sysroot.rs

@@ -240,7 +240,8 @@ fn build_clif_sysroot_for_triple(
     rustflags
         .push_str(&format!(" --sysroot={}", RTSTARTUP_SYSROOT.to_path(dirs).to_str().unwrap()));
     if channel == "release" {
-        rustflags.push_str(" -Zmir-opt-level=3");
+        // FIXME switch back to 3 once https://github.com/rust-lang/rust/issues/108166 is fixed
+        rustflags.push_str(" -Zmir-opt-level=2");
     }
     compiler.rustflags += &rustflags;
     let mut build_cmd = STANDARD_LIBRARY.build(&compiler, dirs);