Rollup merge of #121207 - chriswailes:z-external-clangrt, r=michaelwoerister

Add `-Z external-clangrt`

This adds the unstable `-Z external-clangrt` flag that will prevent rustc from emitting linker paths for the in-tree LLVM sanitizer runtime library.

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1216,20 +1216,29 @@ fn add_sanitizer_libraries(
     crate_type: CrateType,
     linker: &mut dyn Linker,
 ) {
+    if sess.target.is_like_android {
+        // Sanitizer runtime libraries are provided dynamically on Android
+        // targets.
+        return;
+    }
+
+    if sess.opts.unstable_opts.external_clangrt {
+        // Linking against in-tree sanitizer runtimes is disabled via
+        // `-Z external-clangrt`
+        return;
+    }
+
+    if matches!(crate_type, CrateType::Rlib | CrateType::Staticlib) {
+        return;
+    }
+
     // On macOS and Windows using MSVC the runtimes are distributed as dylibs
     // which should be linked to both executables and dynamic libraries.
     // Everywhere else the runtimes are currently distributed as static
     // libraries which should be linked to executables only.
-    let needs_runtime = !sess.target.is_like_android
-        && match crate_type {
-            CrateType::Executable => true,
-            CrateType::Dylib | CrateType::Cdylib | CrateType::ProcMacro => {
-                sess.target.is_like_osx || sess.target.is_like_msvc
-            }
-            CrateType::Rlib | CrateType::Staticlib => false,
-        };
-
-    if !needs_runtime {
+    if matches!(crate_type, CrateType::Dylib | CrateType::Cdylib | CrateType::ProcMacro)
+        && !(sess.target.is_like_osx || sess.target.is_like_msvc)
+    {
         return;
     }
 

compiler/rustc_session/src/options.rs

@@ -1645,6 +1645,8 @@ options! {
         "emit the bc module with thin LTO info (default: yes)"),
     export_executable_symbols: bool = (false, parse_bool, [TRACKED],
         "export symbols from executables, as if they were dynamic libraries"),
+    external_clangrt: bool = (false, parse_bool, [UNTRACKED],
+        "rely on user specified linker commands to find clangrt"),
     extra_const_ub_checks: bool = (false, parse_bool, [TRACKED],
         "turns on more checks to detect const UB, which can be slow (default: no)"),
     #[rustc_lint_opt_deny_field_access("use `Session::fewer_names` instead of this field")]