llext: fix Windows builds

Under windows the Python interpreter has to be called explicitly.
Without it an attempt to execute a Python script fails silently.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>

scripts/xtensa-build-zephyr.py

@@ -945,7 +945,11 @@ def install_lib(sof_lib_dir, abs_build_dir, platform_wconfig):
 			llext_input = entry_path / (llext_base + '.llext')
 			llext_output = entry_path / (llext_file + '.ri')
 
-			sign_cmd = [platform_wconfig.get("rimage.path"), "-o", str(llext_output),
+			# See why the shlex() parsing step is required at
+			# https://docs.zephyrproject.org/latest/develop/west/sign.html#rimage
+			# and in Zephyr commit 030b740bd1ec
+			rimage_cmd = shlex.split(platform_wconfig.get('rimage.path'))[0]
+			sign_cmd = [rimage_cmd, "-o", str(llext_output),
 				    "-e", "-c", str(rimage_cfg),
 				    "-k", str(signing_key), "-l", "-r",
 				    str(llext_input)]

zephyr/CMakeLists.txt

@@ -90,7 +90,7 @@ function(sof_llext_build module)
 	get_target_property(proc_out_file ${module} pkg_input)
 	add_llext_command(TARGET ${module}
 		POST_BUILD
-		COMMAND ${SOF_BASE}scripts/llext_link_helper.py
+		COMMAND ${PYTHON_EXECUTABLE} ${SOF_BASE}scripts/llext_link_helper.py
 			--text-addr="${SOF_LLEXT_TEXT_ADDR}" -f ${proc_in_file} ${CMAKE_C_COMPILER} --
 			-o ${proc_out_file} ${EXTRA_LINKER_PARAMS}
 	                $<TARGET_OBJECTS:${module}_llext_lib>