Port, board and/or hardware

unix port, longlong variant

MicroPython version

local version based on v1.25.0-387-g17fbc5abdc

Reproduction

1. Modify tools.ci.sh to update the longlong build to include ubsan:

   ci_unix_build_helper VARIANT=longlong MICROPY_USE_COMPILER_PLUGIN=gcc \
   CFLAGS_EXTRA="-fsanitize=undefined -fno-sanitize=nonnull-attribute" LDFLAGS_EXTRA="-fsanitize=undefined -fno-sanitize=nonnull-attribute"
   

}

2. `(set -e; . tools/ci.sh; ci_unix_longlong_build; ci_unix_longlong_run_tests)`


### Expected behaviour

Tests succeed

### Observed behaviour

There are failures. Typical failure:

FAILURE /home/jepler/src/micropython/tests/results/basics_int_64_basics.py
--- /home/jepler/src/micropython/tests/results/basics_int_64_basics.py.exp 2025-07-17 12:00:04.723931234 -0500
+++ /home/jepler/src/micropython/tests/results/basics_int_64_basics.py.out 2025-07-17 12:00:04.727931280 -0500
@@ -117,6 +117,7 @@
0
0
left shift negative
+../../py/objint_longlong.c:215:30: runtime error: left shift of negative value -10000000000000000
-10000000000000000
-10000000000000001
-10000000000000002

4 tests failed: basics/int_64_basics.py micropython/viper_ptr32_store_boundary.py micropython/viper_ptr8_store_boundary.py micropython/viper_ptr16_store_boundary.py

### Additional Information

It might be a nice to add sanitizer builds of longlong (& nanbox?).

### Code of Conduct

Yes, I agree