[test] Use new module cache; some diags only occur in module building

Author: jrose-apple

test/ClangImporter/attr-swift_name.swift

@@ -1,4 +1,5 @@
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -I %S/Inputs/custom-modules -Xcc -w -typecheck %s 2>&1 | %FileCheck %s
+// RUN: %empty-directory(%t.mcp)
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -I %S/Inputs/custom-modules -Xcc -w -typecheck %s -module-cache-path %t.mcp 2>&1 | %FileCheck %s
 
 // REQUIRES: objc_interop
 

test/ClangImporter/import-as-member.swift

@@ -1,5 +1,6 @@
-// RUN: not %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-objc-interop -typecheck -F %S/Inputs/frameworks -I %S/Inputs/custom-modules %s 2>&1 | %FileCheck %S/Inputs/custom-modules/ImportAsMember.h
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-objc-interop -typecheck -F %S/Inputs/frameworks -I %S/Inputs/custom-modules %s -verify
+// RUN: %empty-directory(%t.mcp)
+// RUN: not %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-objc-interop -typecheck -F %S/Inputs/frameworks -I %S/Inputs/custom-modules -module-cache-path %t.mcp %s 2>&1 | %FileCheck %S/Inputs/custom-modules/ImportAsMember.h
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-objc-interop -typecheck -F %S/Inputs/frameworks -I %S/Inputs/custom-modules -module-cache-path %t.mcp %s -verify
 
 import ImportAsMember
 import ImportAsMemberSubmodules