Remove usage of -Zno-parallel-llvm

Author: GuillaumeGomez

tests/lang_tests_common.rs

@@ -80,7 +80,6 @@ pub fn main_inner(profile: Profile) {
                 &format!("-Zcodegen-backend={}/target/debug/librustc_codegen_gcc.so", current_dir),
                 "--sysroot",
                 &format!("{}/build/build_sysroot/sysroot/", current_dir),
-                "-Zno-parallel-llvm",
                 "-C",
                 "link-arg=-lc",
                 "-o",