Android: Fix crash caused by unintentionally modification of env data.

The data given to putenv(3) becomes a part of the environment, as
described in SUSv2, so If the data is unintentionally modified or
deleted the consequence can be fatal.
In previous versions of Android, the putenv(3) implementation made a
copy of the data, so this bug has gone unnoticed.

Task-number: QTBUG-39042
Change-Id: I337c483f3927eb35188798ab349cd722999afae9
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>