Update cg_clif to use build.compiletest-force-stage0

Author: jieyouxu

compiler/rustc_codegen_cranelift/scripts/test_rustc_tests.sh

@@ -166,5 +166,5 @@ index 073116933bd..c3e4578204d 100644
 EOF
 
 echo "[TEST] rustc test suite"
-COMPILETEST_FORCE_STAGE0=1 ./x.py test --stage 0 --test-args=--no-capture tests/{codegen-units,run-make,ui,incremental}
+./x.py test --stage=0 --set build.compiletest-force-stage0=true --test-args=--no-capture tests/{codegen-units,run-make,ui,incremental}
 popd