This change is needed to ensure that vk_icdXXX entry points
are exported, as expected by Khronos' Vulkan loader.

Change-Id: I25b232eb3a99767072be198621bda91e3f9f9cbe
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/33050
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: David Turner <digit@google.com>
Presubmit-Ready: David Turner <digit@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>