[clang][python] Don't add check-clang-python to check-all if cross-compiling

Consistent with other cases for these tests, we opt not to add the
target to check-all if they're known to fail. The tests fail when cross
compiling for a different architecture because the host
Python3_EXECUTABLE is used to run them, and FFI calls will of course
fail against the libraries compiled for the target.

This is an alternate take on
<llvm#111367>.

Author: asb

clang/bindings/python/tests/CMakeLists.txt

@@ -47,6 +47,14 @@ if(${LLVM_NATIVE_ARCH} MATCHES "^(AArch64|Hexagon|Sparc|SystemZ)$")
   set(RUN_PYTHON_TESTS FALSE)
 endif()
 
+# Tests will fail if cross-compiling for a different target, as tests will try
+# to use the host Python3_EXECUTABLE and make FFI calls to functions in target
+# libraries.
+if(CMAKE_CROSS_COMPILING)
+  message(WARNING "check-clang-python-tests not added to check-all as they fail in a cross-build setup")
+  set(RUN_PYTHON_TESTS FALSE)
+endif()
+
 if(RUN_PYTHON_TESTS)
     set_property(GLOBAL APPEND PROPERTY
                  LLVM_ALL_ADDITIONAL_TEST_TARGETS check-clang-python)