After installing the latest Visual Studio 2017 15.6.6 (Community Edition), I found my custom setting of environment variables
INCLUDE lost effect in the Developer Command Prompt. Strangely,
LIB was still there. Some tracing indicated that it was a bug in the .BAT files Microsoft provided to initialize the environment. The offending lines are the following (in C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\Tools\vsdevcmd\core\winsdk.bat; one of them is very long and requires scrolling for viewing):
@REM the folowing are architecture neutral set __tmpwinsdk_include= if "%INCLUDE%" NEQ "" set "__tmp_include=;%INCLUDE%" set "INCLUDE=%WindowsSdkDir%include\%WindowsSDKVersion%shared;%WindowsSdkDir%include\%WindowsSDKVersion%um;%WindowsSdkDir%include\%WindowsSDKVersion%winrt;%WindowsSdkDir%include\%WindowsSDKVersion%cppwinrt%__tmpwinsdk_include%" set __tmpwinsdk_include=
Apparently somebody missed renaming
__tmpwinsdk_include. Doing that myself fixed the problem.
I’ve reported the problem to Microsoft. In the meanwhile, you know how to fix it if you encounter the same problem.