Fix Build of clutter-test-utils.c on Windows

The use of "environ" clashes with a #define in Window's stdlib.h, at least
on Visual Studio, so fix the build by prefixing environ with test_.

https://bugzilla.gnome.org/show_bug.cgi?id=725716
Fix The Win32 Backend for Newer Visual Studio Versions

The GetSystemMetrics() function returns wrong values for SM_CXSIZEFRAME,
SM_CYSIZEFRAME, SM_CXFIXEDFRAME and SM_CYFIXEDFRAME when built with Visual
Studio 2012 and 2013 (unless the XP compatibility setting for the
PlatformToolset entry is turned on), causing the window of Clutter programs
to automatically shrink to a point where they become unusable.

This patch uses AdjustWindowRectEx() for builds using Visual Studio 2012
and later, which deduces the required height and width of the Window
properly.  Unfortunately we can't use this for the VS 2008/2010 builds as
they cause the Window to continually expand as the program is run.

https://bugzilla.gnome.org/show_bug.cgi?id=725873