This also fixes running them from within Visual Studio without requiring
setting any environment variables.

Change-Id: I5592b2d6a0abfeaeffbe1b788529c77adf5764ed
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/35629
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>