add a test case for an invalid optimization

A recent optimization was overly aggressive and resulted in a miscompile
in FoundationNetworking.  Add a test case.

Author: compnerd

test-foundation-package/test-foundation-networking.txt

@@ -1,6 +1,12 @@
 REQUIRES: platform=Linux
+
 RUN: rm -rf %t
 RUN: mkdir -p %t
+
 RUN: %{swiftc}  -o %t/test-foundation-networking %S/test-foundation-networking.swift
 RUN: %t/test-foundation-networking | %{FileCheck} %s
+
+RUN: %{swiftc} -O -o %t/test-foundation-networking %S/test-foundation-networking.swift
+RUN: %t/test-foundation-networking | %{FileCheck} %s
+
 CHECK: http://example.com