[ClangCL] Fix warnings on PixTest.cpp (microsoft#5689)

1. signed unisgned compare warning.
  Fixed by change 1 into 1u. Or cast directly.
2. writeable string.
  Use const char/wchar_t * instead of char/wchar_t*.
3. lost const when cast.
   Add const.

Author: python3kgae

include/dxc/Test/DxcTestUtils.h

@@ -217,9 +217,10 @@ void WideToBlob(dxc::DxcDllSupport &dllSupport, const std::wstring &val,
 void WideToBlob(dxc::DxcDllSupport &dllSupport, const std::wstring &val,
                 IDxcBlobEncoding **ppBlob);
 void VerifyCompileOK(dxc::DxcDllSupport &dllSupport, LPCSTR pText,
-                     LPWSTR pTargetProfile, LPCWSTR pArgs, IDxcBlob **ppResult);
+                     LPCWSTR pTargetProfile, LPCWSTR pArgs,
+                    IDxcBlob **ppResult);
 void VerifyCompileOK(dxc::DxcDllSupport &dllSupport, LPCSTR pText,
-                     LPWSTR pTargetProfile, std::vector<LPCWSTR> &args,
+                     LPCWSTR pTargetProfile, std::vector<LPCWSTR> &args,
                      IDxcBlob **ppResult);
 
 HRESULT GetVersion(dxc::DxcDllSupport &DllSupport, REFCLSID clsid,