Also copy the DLLs to build/
This makes it consistent with the CMake build.

Bug b/116336664
Bug b/29024574

Change-Id: I747a52383492c3ec5493f1a232cbbf5c98aec219
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27608
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>