VS 2017 15.4 with 10.0.15063.468 SDK

This change switches the VS 2017 package to use VS 2017 Update 4 while
still using the 10.0.15063.468 SDK. Update 4 fixes at least one code-gen
bug (crbug.com/759402) but the 10.0.16299.0 SDK is still incompatible
with Chrome (crbug.com/773476).

Packaging was done on a Windows Server 2016 VM, cleanly created for this
purpose.

Compiler was packaged up by downloading VS 2017 Update 4, from
https://www.visualstudio.com/vs/, and then passing these parameters to
the installer:

    --add Microsoft.VisualStudio.Workload.NativeDesktop
    --add Microsoft.VisualStudio.Component.VC.ATLMFC --includeRecommended
    --passive

Then the Windows 10.0.15063.468 SDK installer was run and everything was
installed except for the Windows Performance Toolkit, .Net Framework,
and the arm SDKs.

Then the packaging script was run like this:

    python depot_tools\win_toolchain\package_from_installed.py 2017 -w 10.0.15063.0

Bug: 773476,759402
Change-Id: Ie2176b5ff765d9e5497f51a7b00c02fad04fb973
Reviewed-on: https://chromium-review.googlesource.com/727523Reviewed-by: Scott Graham <scottmg@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510207}

build/vs_toolchain.py

@@ -357,8 +357,8 @@ def _GetDesiredVsToolchainHashes():
     # Update 3 final with 10.0.15063.468 SDK and no vctip.exe.
     return ['f53e4598951162bad6330f7a167486c7ae5db1e5']
   if env_version == '2017':
-    # VS 2017 Update 3.2 with 10.0.15063.468 SDK and patched setenv.cmd.
-    return ['a9e1098bba66d2acccc377d5ee81265910f29272']
+    # VS 2017 Update 4 with 10.0.15063.468 SDK.
+    return ['88c3b62e1eb0893b8cd57e3f4859c3af27907f64']
   raise Exception('Unsupported VS version %s' % env_version)