> This wasn't fixed because _decimal didn't build before issue26846 lands.

This is misleading, the problem went unnoticed when not linking with '-lm' because:
* The _decimal extension module builds without any warning.
* test_decimal does not fail.

One way to demonstrate the problem in the interactive interpreter on Android:
>>> import decimal
>>> import _decimal
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: dlopen failed: cannot locate symbol "log10" referenced by "_decimal.cpython-37dm.so"...