src/sage/doctest/control.py: log cysignals crashes to DOT_SAGE

We set CYSIGNALS_CRASH_LOGS="$DOT_SAGE/crash_logs" in sage-env, but
currently, are are overriding that with a temporary directory in the
DocTestController's run_val_gdb() method.

For consistency, it makes more sense to place the doctest crash logs
in the same place as the "regular" crash logs. Doctest crashes are
important too, and if they are worth retaining at all, they are worth
retaining beyond a reboot or ten days (the current systemd
default). On the other hand, if the logs were truly transient, they
could be disabled by setting CYSIGNALS_CRASH_LOGS to an empty value.
Since we are making some effort to save them, they should be
considered more persistent than not.

src/sage/doctest/control.py

@@ -43,7 +43,6 @@
 import sage.misc.randstate as randstate
 from sage.structure.sage_object import SageObject
 from sage.env import DOT_SAGE, SAGE_LIB, SAGE_SRC, SAGE_VENV, SAGE_EXTCODE
-from sage.misc.temporary_file import tmp_dir
 from cysignals.signals import AlarmInterrupt, init_cysignals
 
 from .sources import FileDocTestSource, DictAsObject, get_basename
@@ -1342,9 +1341,10 @@ def run_val_gdb(self, testing=False):
         if testing:
             return
 
-        # Setup signal handlers.
-        # Save crash logs in temporary directory.
-        os.putenv('CYSIGNALS_CRASH_LOGS', tmp_dir("crash_logs_"))
+
+        # Setup signal handlers. Crashes are logged to the directory
+        # specified by CYSIGNALS_CRASH_LOGS, typically set by sage-env
+        # to a subdirectory of DOT_SAGE.
         init_cysignals()
 
         import signal