Disable TestEnvironment on Windows

The input source file seems to be triggering an error in the Visual
Studio headers.

> xstddef:338:2: error: ''auto' return without trailing return type;
> deduced return types are a C++14 extension

I tried converting the test to use the %build stuff Zachary added, but
that seems to be missing some Darwin support. Disabling the test on
Windows in the meantime.

llvm-svn: 360624

lldb/lit/Process/TestEnvironment.test

@@ -1,3 +1,5 @@
+UNSUPPORTED: system-windows
+
 The double quotes around "BAR" ensure we don't match the command.
 
 RUN: %clangxx -std=c++11 %p/Inputs/env.cpp -o %t