ANGLE: Don't export DLLMain functions for static builds

These ifdef guards were originally a part of
"0004-Make-it-possible-to-link-ANGLE-statically-for-single.patch",
but were lost during the last ANGLE upgrade.

Task-number: QTBUG-37842
Change-Id: I4340c1641675dd310c14454a851eb4bc0ae2ec0d
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
d3dcompiler_qt: Directly link the d3dcompiler DLL on WinRT 8.1

The compiler DLL is a system module starting with Windows 8.1, so
directly link to it instead of expecting a packaged DLL. This makes
shader precompilation completely optional on this platform.

Change-Id: I46cd175ac32e4909a518a059721241b1d6e7be17
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@digia.com>