#7418 - circumvent use of timer threads to make WASM integration of z3 easier

The scoped_timer uses a std::therad. Spawning this thread fails in cases of WASM.
Instead of adapting builds and using async features at the level of WASM and the client, we expose a specialized version of z3 that doesn't use threads at all, neither for solvers nor for timers.
The tradeoff is that the periodic poll that checks for timeout directly queries the global clock each time.
We characterize it as based on polling.

src/api/python/setup.py

@@ -30,6 +30,7 @@ ENABLE_LTO = True
 
 IS_PYODIDE = 'PYODIDE_ROOT' in os.environ and os.environ.get('_PYTHON_HOST_PLATFORM', '').startswith('emscripten')
 
+
 # determine where binaries are
 RELEASE_DIR = os.environ.get('PACKAGE_FROM_RELEASE', None)
 if RELEASE_DIR is None:
@@ -133,7 +134,8 @@ def _configure_z3():
     # Config options
     cmake_options = {
         # Config Options
-        'Z3_SINGLE_THREADED' : IS_SINGLE_THREADED,
+        'Z3_SINGLE_THREADED' : IS_SINGLE_THREADED,      # avoid solving features that use threads
+        'Z3_POLING_TIMER' : IS_SINGLE_THREADED,         # avoid using timer threads
         'Z3_BUILD_PYTHON_BINDINGS' : True,
         # Build Options
         'CMAKE_BUILD_TYPE' : 'Release',