#[allow(internal_features)] in RUSTC_BOOTSTRAP test

This will be required in the future (where "the future" is my PR
which fails CI because of cargo here).

tests/testsuite/build_script_env.rs

@@ -117,7 +117,7 @@ fn rustc_bootstrap() {
     "#;
     let p = project()
         .file("Cargo.toml", &basic_manifest("has-dashes", "0.0.1"))
-        .file("src/lib.rs", "#![feature(rustc_attrs)]")
+        .file("src/lib.rs", "#![allow(internal_features)] #![feature(rustc_attrs)]")
         .file("build.rs", build_rs)
         .build();
     // RUSTC_BOOTSTRAP unset on stable should error
@@ -154,7 +154,7 @@ fn rustc_bootstrap() {
     // Tests for binaries instead of libraries
     let p = project()
         .file("Cargo.toml", &basic_manifest("foo", "0.0.1"))
-        .file("src/main.rs", "#![feature(rustc_attrs)] fn main() {}")
+        .file("src/main.rs", "#![allow(internal_features)] #![feature(rustc_attrs)] fn main() {}")
         .file("build.rs", build_rs)
         .build();
     // nightly should warn when there's no library whether or not RUSTC_BOOTSTRAP is set