Fix test/IRGen/keypath_protocol_extension.swift

Fixes rdar://139993108.

Author: slavapestov

test/IRGen/keypath_protocol_extension.swift

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -emit-module %S/Inputs/keypath_protocol_extension_other.swift -emit-module-path %t/keypath_protocol_extension_other.swiftmodule
-// RUN: %target-swift-frontend -emit-ir %s -I %t
+// RUN: %target-swift-frontend -target %target-swift-5.7-abi-triple -emit-ir %s -I %t
 
 import keypath_protocol_extension_other