> (...) things like PGO often require flags that the linker sees in order to generate the instrumented binary. If those are left off of the link step, you won't have an instrumented binary and won't generate profile data.

Oh, I didn't try my PR...

$ ./configure --enable-optimizations
$ make
...
/usr/bin/ld: libpython3.8m.a(myreadline.o):(.data+0xa0): undefined reference to `__gcov_merge_add'
...

My PR simply doesn't work: we have to pass PGO flags to the linker. At least for the first step generating a profile.

My bad, sorry, I close my PR 11219.