It looks like 341e8a939aca6e9f59ffb0e6daee5888933694ed (GH-24549) incorrectly deleted an important check in sysconfig that is needed for building the cpython standard library on unix-y systems. The chain of events is somewhat complicated but the problem can be easily seen by carefully examining the output of a simple build and install, like:

./configure --prefix=/tmp/testbuild
make
make install

As of 3.10.0b1, this results in the standard library module being built twice, once by the make step and once by the make install step.

GH-26237 attempts to fix the problem with minimal changes to the approach taken in GH-24549 to consolidate Lib/sysconfig.py and Lib/distutils/sysconfig.py. Frankly, I am not confident it is the best approach so it should be carefully reviewed. There probably should also be a test added at some point for this case but I will let someone else deal with that and a test should not hold up 3.10.0b2. But I think the build failure is serious enough that b2 should be held for a fix.