Fixed a test failure that occurs when the specified font is not installed.

On systems where 'Liberation Sans' is not installed out-of-the-box
(e.g. Ubuntu Server, OpenSuse Server) it falls back to 'DejaVu Sans',
which makes the GetHashCode_NameDiffers_HashesNotEqual() test fail as
the two font names are now equal. Instead we use 'Arial' and 'Courier New'
which resolve to different fonts on most systems.

Changes licensed under MIT/X11.
[Bug 16267] SemaphoreSlim.Wait fix when no timeout

See https://bugzilla.xamarin.com/show_bug.cgi?id=16267
Check for __readfsdword at configure-time

Recent versions of mingw-w64 have moved this definition to a header
included by this file, so checking simply for GCC would cause a multiple
definition error. We should instead check for this function's
availability at configure-time.

These changes are released under MIT/X11 license.
Merge pull request #813 from ColdPie1/mingw64fix

Check for __readfsdword at configure-time
Merge pull request #810 from criteo/16267-SemaphoreSlim

[Bug 16267] SemaphoreSlim.Wait fix when no timeout
Merge pull request #807 from akoeplinger/fix-fonttest

Fixed a test failure that occurs when the specified font is not installed