compile Vulkan SPIR-V shaders in CMAKE_CURRENT_BINARY_DIR (#2055)

fixes #2040 

* Compiles the Vulkan SPIR-V files in a directory based off of
CMAKE_CURRENT_BINARY_DIR.
* Changes the search path for the Vulkan SPIR-V files to this directory
rather than a semi-arbitrary set of directories.

test_conformance/common/vulkan_wrapper/vulkan_utility.hpp

@@ -72,5 +72,6 @@ operator<<(std::ostream& os,
            VulkanExternalSemaphoreHandleType externalSemaphoreHandleType);
 std::ostream& operator<<(std::ostream& os, VulkanFormat format);
 
-std::vector<char> readFile(const std::string& filename);
+std::vector<char> readFile(const std::string& filename,
+                           const std::string& startdir);
 #endif // _vulkan_utility_hpp_