By setting LD_LIBRARY_PATH to the directory containing
libvk_swiftshader.so, this change enables running vk-unittests
from any working directory.

Bug: b/128618202
Change-Id: Ib10e4742b90a41d1ef9867b59ce2ccb7394e2b02
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/36811
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>