Cross building GLib tests for Windows fails with '"libgio-2.0-0.dll" failed to initialize, aborting'

**Describe the bug**
As reported at https://gitlab.gnome.org/GNOME/glib/-/issues/2573, a cross build for Windows may use potentially inappropriate DLLs when running cross compiled applications.
In the case described, a libglib-2.0-0.dll from a system path was used because corresponding system paths were first contained in the WINEPATH environment variable.

**To Reproduce**
See https://gitlab.gnome.org/GNOME/glib/-/issues/2573

**Expected behavior**
The WINEPATH environment variable must contain the paths to the build directory first and then the system paths.

**system parameters**
* cross build for Windows with gcc
* openSUSE 15.2
* python 3.6.12
* meason version 0.56.2
* ninja version 1.10.2

Start by reproducing the cross build for Windows described in the linked GLib issue and inspect how Meson constructs WINEPATH for test execution. Confirm that build-directory paths precede system paths, then rerun the GLib tests to verify that the intended DLLs are selected.

Written by the indexing model from the issue text.