gmp-compat-test no longer works in GitHub actions or in Docker

[creachadair]

I have not had occasion to run the gmp-compat-test suite in GitHub Actions for a while, and they now no longer work properly when run there. When run, either in a local Docker container or in the Actions worker, the test runner fails in make check with this error:

./genpytest.py > wrappers.py                                                                                                           
./gendata.py > random.tests                                        
./runtest -p 100000 random.tests               
Traceback (most recent call last):                       
  File "/imath/tests/gmp-compat-test/runtest.py", line 115, in <module>
    gmp_test_so = ctypes.cdll.LoadLibrary("gmp_test.so")           
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                               
  File "/usr/lib/python3.12/ctypes/__init__.py", line 460, in LoadLibrary
    return self._dlltype(name)                 
           ^^^^^^^^^^^^^^^^^^^                                     
  File "/usr/lib/python3.12/ctypes/__init__.py", line 379, in __init__
    self._handle = _dlopen(self._name, mode)                                                                                           
                   ^^^^^^^^^^^^^^^^^^^^^^^^^         
OSError: Error relocating ./gmp_test.so: __gmpz_set_si: symbol not found

I thought at first this was a simple link order issue, but that alone was not sufficient to fix it. I thought it might also be an arm64/amd64 issue, but I tried a couple variations of platform and all seem to have the same symptoms in this environment.

For now I've disabled make check in CI, but I should probably figure this out. I'm sure there's some long painful way in which I'm holding it wrong.

[creachadair]

See also #60, which fixes this problem for GitHub Actions.

[creachadair]

It appears the issue is specific to GCC, and that building with clang avoids the problem.