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 <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>

tests/VulkanUnitTests/Driver.cpp

diff --git a/tests/VulkanUnitTests/Driver.cpp b/tests/VulkanUnitTests/Driver.cpp
index d5d40cd..e216d74 100644
--- a/tests/VulkanUnitTests/Driver.cpp
+++ b/tests/VulkanUnitTests/Driver.cpp
@@ -64,15 +64,16 @@
 		#else
 			return load("./build/Release_Win32/vk_swiftshader.dll") ||
 		#endif
-			       load("./build/Release/libvk_swiftshader.dll");
+			       load("./build/Release/libvk_swiftshader.dll") ||
 	#else
 		#if defined(_WIN64)
 			return load("./build/Debug_x64/vk_swiftshader.dll") ||
 		#else
 			return load("./build/Debug_Win32/vk_swiftshader.dll") ||
 		#endif
-			       load("./build/Debug/libvk_swiftshader.dll");
+			       load("./build/Debug/libvk_swiftshader.dll") ||
 	#endif
+			       load("./libvk_swiftshader.dll");
 #elif OS_MAC
 	return load("./build/Darwin/libvk_swiftshader.dylib") ||
 	       load("swiftshader/libvk_swiftshader.dylib") ||