[clang][python] Don't add check-clang-python to check-all if cross-compiling (#111657)

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.

Do note that CMAKE_CROSSCOMPILING is set to true whenever CMAKE_SYSTEM_NAME was set manually <https://cmake.org/cmake/help/latest/variable/CMAKE_CROSSCOMPILING.html> so in some circumstances it may be set even when not cross-compiling. However, it's the best way of checking that CMake has right now, and we use it elsewhere in LLVM's build system.

Author: asb

clang/bindings/python/tests/CMakeLists.txt

@@ -47,6 +47,19 @@ 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_CROSSCOMPILING)
+  # FIXME: Consider a solution that allows better control over these tests in
+  # a crosscompiling scenario. e.g. registering them with lit to allow them to
+  # be explicitly skipped via appropriate LIT_ARGS, or adding a mechanism to
+  # allow specifying a python interpreter compiled for the target that could
+  # be executed using qemu-user.
+  message(WARNING "check-clang-python not added to check-all as these tests 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)