[Tests] Add swift_Concurrency to the LTO workaround.

Kuba reckons this will fix the test hanging.

rdar://84393438

Author: al45tair

test/lit.cfg

@@ -977,15 +977,17 @@ if run_vendor == 'apple':
 
     # Auto-linking does not work when stdlib is built with LTO, because linked
     # libraries are discovered too late (after optimizations are applied), and
-    # ld64 hits an assert and crashes. Until ld64 fixes this, let's workaround
-    # it by explicitly -l linking all libraries needed in tests.
+    # ld64 hits an assert and crashes, or worse, deadlocks. Until ld64 fixes
+    # this, let's workaround it by explicitly -l linking all libraries needed in
+    # tests.
+    # rdar://70787171
     if "stdlib_lto" in config.available_features:
         for library in ["swiftCore", "swiftStdlibUnittest",
                         "swiftStdlibUnicodeUnittest",
                         "swiftStdlibCollectionUnittest",
                         "swiftSwiftPrivateLibcExtras", "swiftSwiftPrivate",
                         "swiftDarwin", "swiftSwiftPrivateThreadExtras",
-                        "swiftSwiftOnoneSupport"]:
+                        "swiftSwiftOnoneSupport", "swift_Concurrency"]:
             swift_execution_tests_extra_flags += ' -Xlinker -l%s'% library
 
         swift_native_clang_tools_path = lit_config.params.get('swift_native_clang_tools_path', None)