build: better error message on python fail

[refack]

Fixes: #16864
Refs: #17293

On a machine without python installed:

d:\code\node$ vcbuild
Could not find python2. More information can be found at
https://github.com/nodejs/node/blob/master/BUILDING.md#windows-1

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

build,windows,tools

[refack]

I suggest this as an alternative to #17293

[refack]

CI: https://ci.nodejs.org/job/node-test-commit-windows-fanned/13781/

[refack]

/CC @nodejs/build @nodejs/platform-windows

[seishun]

This still has the issues I mentioned in #17015 (comment). Namely:

1. run-python is used inconsistently. Most of vcbuild.bat uses :run-python as a replacement for python, but one subroutine uses the VCBUILD_PYTHON_LOCATION variable which it assumes is populated.
2. To make sure the VCBUILD_PYTHON_LOCATION variable is populated (and I guess also to get early exit?), :run-python is called once in the beginning. Now whenever significant changes are introduced into vcbuild.bat, one has to be careful to make sure it's called before the first usage of Python. In fact, this PR already makes a mistake by assuming linting doesn't require Python although it actually does.

[refack]

(2) bug fixed, and made the "validation" section explicit.

What I suggest is that we are gaining more then we're losing. Using run-python gives mostly consistent way to find and call python, and a lower threshold for occasional builders, and building on a new system.
Now that getnodeversion has been moved next to it's usage, it has become an edge case that is run only when building an MSI or doing a release.

[seishun]

The next line uses FULLVERSION which is populated in getnodeversion.

[refack]

Fixed by making the rmdir line more generic.

[seishun]

%TAG% is used in project-gen too.

[refack]

I'll continue working on refactoring the MSI & release bits to a separate batch file, that way we can wrap python, and other dependency resolution in a consistent way, and handle that section differently since is not used by occasional builders.

[bzoz]

Isn't %FULLVERSION% set by getnodeversion?

[bzoz]

Also in :package

[BridgeAR]

Ping @refack

[BridgeAR]

Closing due to long inactivity. @refack please feel free to reopen if you would like to continue working on this!