xtensa-build-zephyr.py: downgrade --cmake-args restriction to a warning

--cmake-args is actually safe, just a bit slower. See explanation in
https://github.com/zephyrproject-rtos/zephyr/pull/56671

Fixes unnecessary restriction added by commit 9fb7a607eb
("xtensa-build-zephyr.py: fix -C option so it can support whitespace")

Also warn for overlays because they act the same.

Log the `west config` due to the suggestion to use build.cmake-args and
the recent rimage changes in Zephyr PR 54700

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

scripts/xtensa-build-zephyr.py

@@ -620,15 +620,21 @@ def build_platforms():
 			overlays = ";".join(overlays)
 			build_cmd.append(f"-DOVERLAY_CONFIG={overlays}")
 
-		# https://docs.zephyrproject.org/latest/guides/west/build-flash-debug.html#one-time-cmake-arguments
-		# https://github.com/zephyrproject-rtos/zephyr/pull/40431#issuecomment-975992951
 		abs_build_dir = pathlib.Path(west_top, platform_build_dir_name)
-		if (pathlib.Path(abs_build_dir, "build.ninja").is_file()
+
-		    or pathlib.Path(abs_build_dir, "Makefile").is_file()):
+		# Longer story in https://github.com/zephyrproject-rtos/zephyr/pull/56671
-			if args.cmake_args and not args.pristine:
+		if not args.pristine and (
-				print(args.cmake_args)
+			pathlib.Path(abs_build_dir, "build.ninja").is_file()
-				raise RuntimeError("Some CMake arguments are ignored in incremental builds, "
+			or pathlib.Path(abs_build_dir, "Makefile").is_file()
-						   + f"you must delete {abs_build_dir} first")
+		):
+			if args.cmake_args or overlays:
+				warnings.warn("""CMake args slow down incremental builds.
+	Passing CMake parameters and overlays on the command line slows down incremental builds
+	see https://docs.zephyrproject.org/latest/guides/west/build-flash-debug.html#one-time-cmake-arguments
+	Try "west config build.cmake-args -- ..." instead.""")
+
+		# Make sure the build logs don't leave anything hidden
+		execute_command(['west', 'config', '-l'], cwd=west_top)
 
 		# Build
 		try: