ci: add a non-PIE build job, the build the 42 machines make #183

On the 42 machines, cc is clang 12 and links non-PIE against Ubuntu 22.04's libreadline 8.1, which is built with -Bsymbolic-functions. On that combination, a readline function taken by address (&rl_forward_char) is the PLT stub. readline's keymaps hold its internal address, so the two never compare equal. Until 3.2 that left every #136 / #140 key unbound on those machines (fixed in #179 by asking readline by name: rl_named_function).

CI builds with gcc as PIE, and the release binary is static musl. Neither can show this class of bug, so the fix has only been proven on a 42 machine.

Proposal: a CI job that builds non-PIE on Ubuntu 22.04 with clang and the system readline:

make all CC=clang EXTRA_CFLAGS=-fno-pie EXTRA_LDFLAGS=-no-pie

It then runs history_prefix_search_test.py, autosuggest_test.py and rl_undo_leak_test.py. On the pre-fix tree (db8f4e3) this job should fail with 57 and 86 failures in the first two.

Caveat: this assumes the hosted runner's clang plus -no-pie reproduces the address split. Check that it fails on db8f4e3 before relying on it.