Initial support for dynamically linked crates

compiler/rustc_session/src/options.rs

@@ -2113,6 +2113,8 @@ options! {
         "emit noalias metadata for box (default: yes)"),
     branch_protection: Option<BranchProtection> = (None, parse_branch_protection, [TRACKED],
         "set options for branch target identification and pointer authentication on AArch64"),
+    build_sdylib_interface: bool = (false, parse_bool, [UNTRACKED],
+        "whether the stable interface is being built"),
     cf_protection: CFProtection = (CFProtection::None, parse_cfprotection, [TRACKED],
         "instrument control-flow architecture protection"),
     check_cfg_all_expected: bool = (false, parse_bool, [UNTRACKED],