Don't require test wrappers to preserve environment variables, use more consistent environment

[Joseph S. Myers]

On Sat, 14 Jun 2014, Andreas Schwab wrote:

> This breaks backward compatibility.

Yes, that's my understanding of what was requested in 
<https://sourceware.org/ml/libc-alpha/2014-05/msg00715.html>: "a simple 
rule that no magic environment bits from the build host implicitly affect 
the test host".

-- 
Joseph S. Myers
joseph@codesourcery.com