Tests: Use split-file to clean up client_reuse_spi.swift.

This results in clearer source locations for diagnostics.

Author: tshortli

test/SPI/client_reuse_spi.swift

@@ -1,29 +1,27 @@
 /// A module should be able to leak SPI types from an import through SPI decls
 
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend -emit-module -DLIB_A %s -module-name A -emit-module-path %t/A.swiftmodule
-// RUN: %target-swift-frontend -emit-module -DLIB_B %s -module-name B -emit-module-path %t/B.swiftmodule -I %t
-// RUN: %target-swift-frontend -typecheck -verify -verify-ignore-unknown -DLIB_C %s -I %t
+// RUN: split-file %s %t
+// RUN: %target-swift-frontend -emit-module %t/A.swift -module-name A -emit-module-path %t/A.swiftmodule
+// RUN: %target-swift-frontend -emit-module %t/B.swift -module-name B -emit-module-path %t/B.swiftmodule -I %t
+// RUN: %target-swift-frontend -typecheck -verify -verify-ignore-unknown %t/C.swift -I %t
 
-#if LIB_A
-// expected-note@-1{{add import of module 'A'}}{{1-1=@_spi(A) import A\n}}
+//--- A.swift
 @_spi(A) public struct SecretStruct {
   @_spi(A) public func bar() {}
 }
 
-#elseif LIB_B
+//--- B.swift
 
 @_spi(A) import A
 
 @_spi(B) public func foo() -> SecretStruct { fatalError() }
 
-#elseif LIB_C
+//--- C.swift
 
 @_spi(B) import B
-
+// expected-note{{add import of module 'A'}}{{1-1=@_spi(A) import A\n}}
 var a = foo() // OK
 a.bar() // expected-error{{instance method 'bar()' is not available due to missing import of defining module 'A'}}
 
 var b = SecretStruct() // expected-error{{cannot find 'SecretStruct' in scope}}
-
-#endif