Use Wide String variants explicitly for Windows API calls (microsoft#7236)

This PR changes some code in ExecutionTests.cpp to use the wide string
variants of Windows API calls explicitly. This is because some internal
builds will get confused about which overload to resolve the
GetModuleHandle function to. By being explicit, this should eliminate
the error that an arg can't be converted to LPCWSTR.

Cherry picked from
microsoft#7235

(cherry picked from commit 2399215)

Author: bob80905

tools/clang/unittests/HLSLExec/ExecutionTest.cpp

@@ -820,10 +820,10 @@ class ExecutionTest {
         return false;
       }
 
-      if (GetModuleHandle("d3d10warp.dll") != NULL) {
-        CHAR szFullModuleFilePath[MAX_PATH] = "";
-        GetModuleFileName(GetModuleHandle("d3d10warp.dll"),
-                          szFullModuleFilePath, sizeof(szFullModuleFilePath));
+      if (GetModuleHandleW(L"d3d10warp.dll") != NULL) {
+        WCHAR szFullModuleFilePath[MAX_PATH] = L"";
+        GetModuleFileNameW(GetModuleHandleW(L"d3d10warp.dll"),
+                           szFullModuleFilePath, sizeof(szFullModuleFilePath));
         WEX::Logging::Log::Comment(WEX::Common::String().Format(
             L"WARP driver loaded from: %S", szFullModuleFilePath));
       }