[cxx-interop] Enable use-std-optional test on Linux

Author: egorzhdan

test/Interop/Cxx/stdlib/use-std-optional.swift

@@ -1,7 +1,7 @@
 // RUN: %target-run-simple-swift(-I %S/Inputs -Xfrontend -enable-experimental-cxx-interop -Xcc -std=c++17 -Xfrontend -validate-tbd-against-ir=none)
 //
 // REQUIRES: executable_test
-// REQUIRES: OS=macosx
+// REQUIRES: OS=macosx || OS=linux-gnu
 
 import StdlibUnittest
 import StdOptional