[clang] [clang][python][test] Check if libclang.so is loadable (PR #142353)

[Rainer Orth via cfe-commits]

rorth wrote:

> @rorth Now that #142371 is merged, can you re-evaluate this PR and update the description?

This PR changed the output from completely silent to excessively verbose: I now get
```
FAILED: tools/clang/bindings/python/tests/CMakeFiles/check-clang-python /var/llvm/local-i386-release-stage2-A-openmp/tools/clang/stage2-bins/tools/clang/bindings/python/tests/CMakeFiles/check-clang-python
cd /vol/llvm/src/llvm-project/local/clang/bindings/python && /usr/bin/cmake -E env CLANG_NO_DEFAULT_CONFIG=1 CLANG_LIBRARY_PATH=/var/llvm/local-i386-release-stage2-A-openmp/tools/clang/stage2-bins/lib /usr/bin/python3.11 -m unittest discover
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE.E.EEEEEEEEE..EEEEEE.EEEEEEEEEEEEEE...EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
======================================================================
ERROR: test_access_specifiers (tests.cindex.test_access_specifiers.TestAccessSpecifiers.test_access_specifiers)
Ensure that C++ access specifiers are available on cursors
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/vol/llvm/src/llvm-project/local/clang/bindings/python/clang/cindex.py", line 4371, in get_cindex_library
    library = cdll.LoadLibrary(self.get_filename())
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/ctypes/__init__.py", line 454, in LoadLibrary
    return self._dlltype(name)
           ^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/ctypes/__init__.py", line 376, in __init__
    self._handle = _dlopen(self._name, mode)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^
OSError: ld.so.1: python3.11: /var/llvm/local-i386-release-stage2-A-openmp/tools/clang/stage2-bins/lib/libclang.so: wrong ELF class: ELFCLASS32

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/vol/llvm/src/llvm-project/local/clang/bindings/python/tests/cindex/test_access_specifiers.py", line 17, in test_access_specifiers
    tu = get_tu(
         ^^^^^^^
  File "/vol/llvm/src/llvm-project/local/clang/bindings/python/tests/cindex/util.py", line 30, in get_tu
    return TranslationUnit.from_source(name, args, unsaved_files=[(name, source)])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/vol/llvm/src/llvm-project/local/clang/bindings/python/clang/cindex.py", line 3317, in from_source
    index = Index.create()
            ^^^^^^^^^^^^^^
  File "/vol/llvm/src/llvm-project/local/clang/bindings/python/clang/cindex.py", line 3189, in create
    return Index(conf.lib.clang_createIndex(excludeDecls, 0))
                 ^^^^^^^^
  File "/vol/llvm/src/llvm-project/local/clang/bindings/python/clang/cindex.py", line 250, in __get__
    value = self.wrapped(instance)
            ^^^^^^^^^^^^^^^^^^^^^^
  File "/vol/llvm/src/llvm-project/local/clang/bindings/python/clang/cindex.py", line 4343, in lib
    lib = self.get_cindex_library()
          ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/vol/llvm/src/llvm-project/local/clang/bindings/python/clang/cindex.py", line 4378, in get_cindex_library
    raise LibclangError(msg)
clang.cindex.LibclangError: ld.so.1: python3.11: /var/llvm/local-i386-release-stage2-A-openmp/tools/clang/stage2-bins/lib/libclang.so: wrong ELF class: ELFCLASS32. To provide a path to libclang use Config.set_library_path() or Config.set_library_file().
```
158 times total.  While one can see what's going on, there's no way to avoid the issue.

https://github.com/llvm/llvm-project/pull/142353