ASSERT "vsyscall incorrect assumption" on AMD 32-bit

This is now showing up on the GA CI VM's since they now use AMD hardware.

Xref DynamoRIO/dynamorio#6417 where 32-bit AMD machines added to GA CI caused a lot of test
failures. This looks similar.

https://github.com/DynamoRIO/drmemory/actions/runs/7515048417/job/20458582246?pr=2490
```
15: ~~Dr.M~~ ASSERT FAILURE (thread 43342):
15: /home/runner/work/drmemory/drmemory/drsyscall/drsyscall_linux.c:239:
15: !is_using_sysint() (vsyscall incorrect assumption)
```

This ends up with these 32-bit debug tests failing beyond the ignored ones on the ci-x86 and ci-clang suites:
```
drmemory-dbg-32: 113 tests passed, **** 11 tests failed, but ignoring 6 for i1938: ****
selfmod
clone
syscalls_unix
pthread_test
realloc
```