As of Python 2.4, some code got added to the
bdist_wininst command to override the build_lib option
on the build command. I had successfully been using the
following command which now fails:

D:\Python24\python.exe setup.py build --force
--compiler=mingw32 --build-lib
D:\Anthony\Build\Dev\cx_Oracle\HEAD\9i-py24\win32
--build-temp
D:\Anthony\Build\Dev\cx_Oracle\HEAD\9i-py24\win32
bdist_wininst --bdist-dir
D:\Anthony\Build\Dev\cx_Oracle\HEAD\9i-py24\win32\temp
--dist-dir
D:\Anthony\Build\Dev\cx_Oracle\HEAD\9i-py24\win32

Here is the offending code from the run() method of the
bdist_wininst command:

        if self.distribution.has_ext_modules():
            # If we are building an installer for a
Python version other
            # than the one we are currently running,
then we need to ensure
            # our build_lib reflects the other Python
version rather than ours.             # Note that for
target_version!=sys.version, we must have skipped the
            # build step, so there is no issue with
enforcing the build of this
            # version.
            target_version = self.target_version
            if not target_version:
                assert self.skip_build, "Should have
already checked this"
                target_version = sys.version[0:3]
            plat_specifier = ".%s-%s" %
(get_platform(), target_version)
            build = self.get_finalized_command('build')
            build.build_lib =
os.path.join(build.build_base,
                                           'lib' +
plat_specifier)

The last line is the problem here. If I comment it out,
the problem goes away.

This problem also occurs in the bdist_msi command.

This is exactly the same problem I was having with bdist_msi.

The offending code appears to have been introduced in r33090 and tweaked
in r37025, which both originated from Mark Hammond.

From the comments, there seems to be no reason why the build_lib
override should apply when the target version is specifically different
from the version being used to build the extension, hence I've attached
a patch which applies the override only when the versions are different
(for both bdist_wininst and bdist_msi).

This doesn't solve the problem that exists when the target and build
versions are different and build_lib has been overridden in setup.py (as
I understand is the case with cx_Oracle).

I've added Mark to the nosy list in the hope he might, as originator of
the problematic changes, be able to provide some insight.

So it looks like I broke the ability to override --build-lib :(  Without
testing, I think you might also need to handle the cross-compile case -
the version may be the same, but the platform different.  I know
distutils is a PITA so might make this difficult, but it might be better
that we only set build_lib if the user didn't - ie, trust the user knows
what they are doing if they specify that option, even in these
'mismatched version/platform' cases.

The distutils bdist_wininst command has been removed in Python 3.10: see bpo-42802.