Support running Vulkan unit tests from the output directory
Support running Vulkan unit tests from the output directory

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 <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Reviewed-by: Ben Clayton <1f693eb7158dc33015048c09d6712f74dabddf79@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Kokoro-Presubmit: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

google/swiftshader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader