Fix find GPU driver dll path in windows (#5141)

docs/developer-guide/vulkan-driver-loader.md

@@ -73,12 +73,12 @@ Requires static meltvk driver linking and should always succeed
 If failed, it will try to find graphics driver object and load it
 
 #### Windows
-search ```C:\Windows\System32\DriverStore\FileRepository``` for
+for 64bit applications. search in ```%SystemRoot%\System32\DriverStore\FileRepository```
 - nvoglv64.dll
 - amdvlk64.dll
 - igvk64.dll
 
-for 32bit applications
+for 32bit applications. search in ```%SystemRoot%\System32\DriverStore\FileRepository```
 - nvoglv32.dll
 - amdvlk32.dll
 - igvk32.dll

src/simplevk.cpp

@@ -554,8 +554,8 @@ int load_vulkan_driver(const char* driver_path)
         for (int i = 0; i < well_known_path_count; i++)
         {
 #if defined _WIN32
-            // find driver dll in C:\\Windows\\System32\\DriverStore\\FileRepository
-            std::string dllpath = search_file("C:\\Windows\\System32\\DriverStore\\FileRepository", well_known_path[i]);
+            // find driver dll in %SystemRoot%\System32\DriverStore\FileRepository  (32bit and 64bit both and in here)
+            std::string dllpath = search_file("%SystemRoot%\\System32\\DriverStore\\FileRepository", well_known_path[i]);
             if (dllpath.empty())
                 continue;