Dockerfile: fix cp clang-extdef-mapping no effect
Use a wrong command `CMD`, and the correct is `RUN`.
That's a low level fault made by me.
@@ -308,7 +308,7 @@ ENV PATH="/tools/rust/cargo/bin:$PATH"
# ARM toolchain
COPY --from=nuttx-toolchain-arm /tools/clang-arm-none-eabi/ clang-arm-none-eabi/
-CMD cp /usr/bin/clang-extdef-mapping-10 clang-arm-none-eabi/bin/clang-extdef-mapping
+RUN cp /usr/bin/clang-extdef-mapping-10 clang-arm-none-eabi/bin/clang-extdef-mapping
ENV PATH="/tools/clang-arm-none-eabi/bin:$PATH"
COPY --from=nuttx-toolchain-arm /tools/gcc-arm-none-eabi/ gcc-arm-none-eabi/
