Revert "[cxx-interop] Partially disable a test on Linux"

This reverts commit ff5b698.

Author: egorzhdan

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

@@ -14,11 +14,9 @@ StdOptionalTestSuite.test("pointee") {
   let pointee = nonNilOpt.pointee
   expectEqual(123, pointee)
 
-#if !os(Linux) // crashes on Ubuntu 18.04 (rdar://113414160)
   var modifiedOpt = getNilOptional()
   modifiedOpt.pointee = 777
   expectEqual(777, modifiedOpt.pointee)
-#endif
 }
 
 StdOptionalTestSuite.test("std::optional => Swift.Optional") {