[embedded] Use %lto_flags in the LTO test in once.swift

Author: kubamracek

test/embedded/once.swift

@@ -1,6 +1,6 @@
 // RUN: %target-run-simple-swift(%S/Inputs/print.swift -enable-experimental-feature Embedded -parse-as-library -runtime-compatibility-version none -wmo -Xfrontend -disable-objc-interop) | %FileCheck %s
 // RUN: %target-run-simple-swift(-O %S/Inputs/print.swift -enable-experimental-feature Embedded -parse-as-library -runtime-compatibility-version none -wmo -Xfrontend -disable-objc-interop) | %FileCheck %s
-// RUN: %target-run-simple-swift(-O -lto=llvm-full %S/Inputs/print.swift -enable-experimental-feature Embedded -parse-as-library -runtime-compatibility-version none -wmo -Xfrontend -disable-objc-interop) | %FileCheck %s
+// RUN: %target-run-simple-swift(-O -lto=llvm-full %lto_flags %S/Inputs/print.swift -enable-experimental-feature Embedded -parse-as-library -runtime-compatibility-version none -wmo -Xfrontend -disable-objc-interop) | %FileCheck %s
 
 // REQUIRES: executable_test
 // REQUIRES: optimized_stdlib