[issue38989] pip install selects 32 bit wheels for 64 bit python if vcvarsall.bat amd64_x86 in environment

[Ryan Thornton]

New submission from Ryan Thornton <thornto4 at gmail.com>:

## Expected Behavior

pip install should download dependencies matching the architecture of the python executable being used.

## Actual Behavior

When calling pip install from a Visual Studio command prompt configured to cross compile from x64 to x86, pip installs wheels matching the architecture of Visual Studio's cross compile target (i.e. `VSCMD_ARG_TGT_ARCH=x86`) and not the architecture of python itself (x64).

This results in a broken installation of core libraries.

## Steps to Reproduce

System Details:
Windows 10 x64
Python 3.8 x64
Visual Studio 2017 15.9.14

Environment Details:
vcvarsall.bat amd64_x86

1. "C:\Program Files\Python38\python.exe" -mvenv "test"
2. cd test\Scripts
3. pip install cffi==1.13.2

Results in the following:

> Collecting cffi
>  Using cached https://files.pythonhosted.org/packages/f8/26/5da5cafef77586e4f7a136b8a24bc81fd2cf1ecb71b6ec3998ffe78ea2cf/cffi-1.13.2-cp38-cp38-win32.whl

## Context

I think the regression was introduced here:
62dfd7d6fe11bfa0cd1d7376382c8e7b1275e38c

https://github.com/python/cpython/commit/62dfd7d6fe11bfa0cd1d7376382c8e7b1275e38c

----------
components: Distutils
messages: 357936
nosy: Ryan Thornton, dstufft, eric.araujo
priority: normal
severity: normal
status: open
title: pip install selects 32 bit wheels for 64 bit python if vcvarsall.bat amd64_x86 in environment
type: behavior
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38989>
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