Check for existence and version of symsrv.dll

The Windows 10 Anniversary Edition of WPA requires that symsrv.dll from
the Debuggers directory be installed. This will normally happen
automatically (when the Windows SDK or VS 2015 are installed) but it is
not actually guaranteed. This adds checks for the existence and a
minimum version of symsrv.dll in the Debuggers directory.

If a significant number of people hit this check then I could bundle
the installers, but for now I'm not going to because I don't want to
add another 26 MB to the release zip files.

Author: Bruce Dawson

UIforETW/UIforETWDlg.cpp

@@ -267,6 +267,30 @@ void CUIforETWDlg::CheckSymbolDLLs()
 
 	if (!filePaths.empty())
 		DeleteFiles(*this, filePaths);
+
+#if defined(_WIN64)
+	const std::wstring symsrv_path = CanonicalizePath(wpt10Dir_ + L"..\\Debuggers\\x64\\symsrv.dll");
+#else
+	const std::wstring symsrv_path = CanonicalizePath(wpt10Dir_ + L"..\\Debuggers\\x86\\symsrv.dll");
+#endif
+	if (!PathFileExists(symsrv_path.c_str()))
+	{
+		AfxMessageBox((L"symsrv.dll (" + symsrv_path +
+			L") not found. Be sure to install the Windows 10 Anniversary Edition Debuggers "
+			L"or else symbol servers will not work.").c_str());
+	}
+
+	// Previous versions of symsrv.dll may not be multithreading safe and therefore can't
+	// be used with the latest WPA.
+	const int64_t requiredSymsrvVersion = (10llu << 48) + 0 + (14321llu << 16) + (1024llu << 0);
+	auto symsrvVersion = GetFileVersion(symsrv_path);
+	if (symsrvVersion < requiredSymsrvVersion)
+	{
+		AfxMessageBox((L"symsrv.dll (" + symsrv_path +
+			L") is not the required version (10.0.14321.1024 or higher). "
+			L"Be sure to install the Windows 10 Anniversary Edition Debuggers "
+			L"or else symbol servers will not work.").c_str());
+	}
 }
 
 BOOL CUIforETWDlg::OnInitDialog()