Add -Zsplit-metadata CLI option

Author: Kobzol

compiler/rustc_interface/src/tests.rs

@@ -859,6 +859,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(simulate_remapped_rust_src_base, Some(PathBuf::from("/rustc/abc")));
     tracked!(small_data_threshold, Some(16));
     tracked!(split_lto_unit, Some(true));
+    tracked!(split_metadata, true);
     tracked!(src_hash_algorithm, Some(SourceFileHashAlgorithm::Sha1));
     tracked!(stack_protector, StackProtector::All);
     tracked!(teach, true);

compiler/rustc_session/src/options.rs

@@ -2482,6 +2482,8 @@ written to standard error output)"),
                   by the linker"),
     split_lto_unit: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "enable LTO unit splitting (default: no)"),
+    split_metadata: bool = (false, parse_bool, [TRACKED],
+        "split metadata out of libraries into .rmeta files"),
     src_hash_algorithm: Option<SourceFileHashAlgorithm> = (None, parse_src_file_hash, [TRACKED],
         "hash algorithm of source files in debug info (`md5`, `sha1`, or `sha256`)"),
     #[rustc_lint_opt_deny_field_access("use `Session::stack_protector` instead of this field")]