I'm seeing this on a rebuild now of Python 3.7.4 on Ubuntu 18.04 (in my case against _ssl.c).

What's happening is there's coverage/profiling data being generated in the build chain (somewhere), which spits out files named *.gcda. Interestingly, make clean does *not* clean these files up.

gcc is attempting to use this data in its optimization, but discovers that it's now bogus -- likely due to system library headers (like OpenSSL) being updated in the meantime, with some inline code causing the coverage data to become invalid.

The fix should be to have 'make clean' clean up these *.gcda files. In the meantime, the workaround is to run "find . -name \*.gcda -exec rm '{}' \;"