Change how standard_lib tests work

* Minimize the sysroot crates in play
* Don't use build scripts to inject args
* Use `RUSTC_WRAPPER` to dynamically switch `--sysroot` depending on
  whether we're building sysroot crates or not.
* Minimize dependency graph in sysroot, only have each crate depend on a
  dummy crates.io crate for testing and otherwise don't depend on
  anything to load the desired sysroot crate directly.

Author: alexcrichton

tests/testsuite/mock-std/Cargo.toml

@@ -1,9 +1,8 @@
 [workspace]
 members = [
+  "src/liballoc",
+  "src/libcore",
+  "src/libproc_macro",
+  "src/libstd",
   "src/libtest",
 ]
-
-[patch.crates-io]
-rustc-std-workspace-std = { path = 'src/tools/rustc-std-workspace-std' }
-rustc-std-workspace-core = { path = 'src/tools/rustc-std-workspace-core' }
-rustc-std-workspace-alloc = { path = 'src/tools/rustc-std-workspace-alloc' }

tests/testsuite/mock-std/src/liballoc/Cargo.toml

@@ -8,4 +8,4 @@ edition = "2018"
 path = "lib.rs"
 
 [dependencies]
-core = { path = "../libcore" }
+registry-dep-using-core = { version = "*", features = ['mockbuild'] }

tests/testsuite/mock-std/src/liballoc/lib.rs

@@ -1 +1,11 @@
-pub fn custom_api() {}
+#![feature(staged_api)]
+#![stable(since = "1.0.0", feature = "dummy")]
+
+extern crate alloc;
+
+#[stable(since = "1.0.0", feature = "dummy")]
+pub use alloc::*;
+
+#[stable(since = "1.0.0", feature = "dummy")]
+pub fn custom_api() {
+}

tests/testsuite/mock-std/src/libcompiler_builtins/Cargo.toml

@@ -6,6 +6,3 @@ edition = "2018"
 
 [lib]
 path = "lib.rs"
-
-[dependencies]
-core = { path = "../libcore" }

tests/testsuite/mock-std/src/libcore/build.rs

@@ -1,4 +1,9 @@
-#![no_std]
+#![feature(staged_api)]
+#![stable(since = "1.0.0", feature = "dummy")]
+
+#[stable(since = "1.0.0", feature = "dummy")]
 pub use core::*;
 
-pub fn custom_api() {}
+#[stable(since = "1.0.0", feature = "dummy")]
+pub fn custom_api() {
+}

tests/testsuite/mock-std/src/libcore/lib.rs

@@ -6,6 +6,3 @@ edition = "2018"
 
 [lib]
 path = "lib.rs"
-
-[dependencies]
-core = { path = "../libcore" }

tests/testsuite/mock-std/src/libpanic_unwind/Cargo.toml

@@ -6,6 +6,3 @@ edition = "2018"
 
 [lib]
 path = "lib.rs"
-
-[dependencies]
-std = { path = "../libstd" }

tests/testsuite/mock-std/src/libproc_macro/Cargo.toml

@@ -1,3 +1,11 @@
+#![feature(staged_api)]
+#![stable(since = "1.0.0", feature = "dummy")]
+
 extern crate proc_macro;
+
+#[stable(since = "1.0.0", feature = "dummy")]
 pub use proc_macro::*;
-pub fn custom_api() {}
+
+#[stable(since = "1.0.0", feature = "dummy")]
+pub fn custom_api() {
+}

tests/testsuite/mock-std/src/libproc_macro/lib.rs

@@ -8,8 +8,4 @@ edition = "2018"
 path = "lib.rs"
 
 [dependencies]
-core = { path = "../libcore" }
-compiler_builtins = { path = "../libcompiler_builtins" }
-panic_unwind = { path = "../libpanic_unwind" }
-registry-dep-using-core = { version = "1.0", features = ['mockbuild'] }
-registry-dep-using-alloc = { version = "1.0", features = ['mockbuild'] }
+registry-dep-using-alloc = { version = "*", features = ['mockbuild'] }