Build without LLVM backend leads to Python Taichi unusable

[k-ye]

Describe the bug

ti
Traceback (most recent call last):
  File "/home/yekuang/miniconda3/envs/taichi-dev/bin/ti", line 33, in <module>
    sys.exit(load_entry_point('taichi', 'console_scripts', 'ti')())
  File "/home/yekuang/miniconda3/envs/taichi-dev/bin/ti", line 25, in importlib_load_entry_point
    return next(matches).load()
  File "/home/yekuang/miniconda3/envs/taichi-dev/lib/python3.9/importlib/metadata.py", line 77, in load
    module = import_module(match.group('module'))
  File "/home/yekuang/miniconda3/envs/taichi-dev/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 972, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 850, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "/home/yekuang/Github/taichi/python/taichi/__init__.py", line 3, in <module>
    from taichi._funcs import *
  File "/home/yekuang/Github/taichi/python/taichi/_funcs.py", line 3, in <module>
    from taichi.lang import impl, matrix, ops
  File "/home/yekuang/Github/taichi/python/taichi/lang/__init__.py", line 1, in <module>
    from taichi.lang import impl, simt
  File "/home/yekuang/Github/taichi/python/taichi/lang/impl.py", line 6, in <module>
    from taichi._lib import core as _ti_core
  File "/home/yekuang/Github/taichi/python/taichi/_lib/__init__.py", line 1, in <module>
    from taichi._lib.utils import ti_core as core
  File "/home/yekuang/Github/taichi/python/taichi/_lib/utils.py", line 165, in <module>
    _print_taichi_header()
  File "/home/yekuang/Github/taichi/python/taichi/_lib/utils.py", line 150, in _print_taichi_header
    llvm_version = ti_core.get_llvm_version_string()
AttributeError: module 'taichi._lib.core.taichi_core' has no attribute 'get_llvm_version_string'

This makes AOT really hard to use, as I have to switch between Taichi with and without LLVM. Let's make this one of the goals #4832 can resolve as well.

[k-ye]

Similar to #5112

[qiao-bo]

close this as fixed by #5113