[M5+] swap toolchain to gcc15Stdenv + libstdc++

src/linkdb/linkdb.cppm

@@ -14,12 +14,6 @@ struct Recipe {
     std::string find_package; // post-substitution
     std::vector<std::string> targets; // post-substitution
     std::string source; // 'curated' | 'manual' | etc.
-    // Set when the dep needs `.override { stdenv = llvmPkgs.libcxxStdenv; }`
-    // to link against the user's libc++-built project (e.g. nixpkgs ships
-    // it built against libstdc++ — abseil-cpp, llvm). verify_link toggles
-    // this on after a libstdc++/libc++ link failure. Codegen wraps the
-    // buildInputs entry in the override expression when true.
-    bool requires_libcxx_override = false;
 
     bool operator==(const Recipe&) const = default;
 };
@@ -43,7 +37,6 @@ struct OverlayRow {
     std::vector<std::string> targets;
     std::string source;
     std::int64_t verified_at = 0;
-    bool requires_libcxx_override = false;
 };
 
 // RAII wrapper for an open sqlite3 connection used by the overlay database.
@@ -97,13 +90,6 @@ auto overlay_delete_recipe(OverlayState& state, const std::string& package,
                            const std::string& source)
     -> cargoxx::util::Result<void>;
 
-// Toggle the libcxx-override flag for an existing row. Used by
-// `verify_link` after a libstdc++/libc++ link mismatch.
-auto overlay_set_libcxx_override(OverlayState& state, const std::string& package,
-                                 const std::string& version_range,
-                                 const std::string& source, bool value)
-    -> cargoxx::util::Result<void>;
-
 // Drops every overlay row for `package` whose source is not "manual".
 // Used by `cargoxx add` to invalidate stale auto-discovered recipes
 // when the resolver/scanner logic has changed under the user — they
@@ -146,11 +132,6 @@ class Database {
                            const std::string& version_range,
                            const std::string& source) -> util::Result<void>;
 
-    auto set_libcxx_override(const std::string& package,
-                             const std::string& version_range,
-                             const std::string& source, bool value)
-        -> util::Result<void>;
-
     // Evict every non-manual overlay row for `package`. Called by
     // `cargoxx add` so users never have to manually drop stale
     // auto-discovered recipes when cargoxx's resolver/scanner logic