Improve error message when debuggers not installed

build/vs_toolchain.py

Index: build/vs_toolchain.py
diff --git a/build/vs_toolchain.py b/build/vs_toolchain.py
index 8c7d6b99b01a04d787715fea12fca6fa42d118e1..b499255290b2f336a2e5118fe01c5ee457cb8513 100755
--- a/build/vs_toolchain.py
+++ b/build/vs_toolchain.py
@@ -325,6 +325,10 @@ def _CopyDebugger(target_dir, target_cpu):
 
   debug_file = 'dbghelp.dll'
   full_path = os.path.join(win_sdk_dir, 'Debuggers', target_cpu, debug_file)
+  if not os.path.exists(full_path):
+    raise Exception('dbghelp.dll not found in "%s"\r\nYou must install the '
+                    '"Debugging Tools for Windows" feature from the Windows '
+                    '10 SDK.' % full_path)

[wkorman, 2017/05/01 18:40:19]

Is there a page worth linking to directly? I found four from Google searching,
with varying dead links, these look like the two that I might explore:

https://developer.microsoft.com/en-us/windows/hardware/windows-driver-kit
https://developer.microsoft.com/en-us/windows/hardware/download-windbg

I realize the urls change often so maybe it's not worth including but thought
worth brief discussion. Since I think the way I probably got into trouble is
that one of the above is the right one, but even now I am not sure which.

And maybe VS 2017 even has an in-app checkbox that in theory installs the thing,
separate from above two urls/installers, but I am not sure that worked for me
per previous bug discussion.

   target_path = os.path.join(target_dir, debug_file)
   _CopyRuntimeImpl(target_path, full_path)