Disable some tests that will fail on back deployment library configurations

rdar://76567524
rdar://76567105

Author: aschwaighofer

test/Interpreter/multi_payload_extra_inhabitant.swift

@@ -9,6 +9,7 @@
 
 // REQUIRES: executable_test
 // UNSUPPORTED: use_os_stdlib
+// UNSUPPORTED: back_deployment_runtime
 
 // CHECK-NOT: Type verification
 

test/Interpreter/struct_extra_inhabitants.swift

@@ -13,6 +13,7 @@
 
 // REQUIRES: executable_test
 // UNSUPPORTED: use_os_stdlib
+// UNSUPPORTED: back_deployment_runtime
 
 // CHECK-NOT: Type verification
 

test/Runtime/demangleToMetadata.swift

@@ -5,6 +5,7 @@
 // REQUIRES: executable_test
 // REQUIRES: concurrency
 // UNSUPPORTED: use_os_stdlib
+// UNSUPPORTED: back_deployment_runtime
 
 import Swift
 import StdlibUnittest

test/lit.cfg

@@ -1569,6 +1569,10 @@ ENV_VAR_PREFIXES = {
 }
 TARGET_ENV_PREFIX = ENV_VAR_PREFIXES.get(config.target_sdk_name, "") if not kIsAndroid else ""
 
+back_deployment_runtime = lit_config.params.get('back_deployment_runtime', None)
+if back_deployment_runtime is not None:
+    config.available_features.add('back_deployment_runtime')
+
 if 'remote_run_host' in lit_config.params:
     if 'remote_run_tmpdir' not in lit_config.params:
         lit_config.fatal("'remote_run_host' provided, but no "