A few files inside the D3D11 tree are used by D3D9 and WGL backends. We
add these files to the build system even when D3D11 is disabled.

Also, we fix the use the of ANGLE_DEFAULT_D3D11 symbol.

Bug: angleproject:4839
Change-Id: I981f4bfc60d973c02549caa737c5aed5ccf31282
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2298143Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>