Fix GCC optimization guards for Clang

[ricardoasouz]

Fixes #205

Clang defines __GNUC__ for GCC compatibility, but it does not support the GCC-specific optimize attribute and #pragma GCC optimize used in these code paths.

This change excludes Clang from the GCC-only optimization hints and also adds the missing IAR guard for arm_depthwise_conv_s8.c.

Validation:

• Reproduced the Clang warnings for both the optimize attribute and #pragma GCC optimize.
• Verified the guards remain enabled for GCC.
• Verified the guards are disabled for Clang.
• Completed the official CMSIS-NN Cortex-M33 GCC build successfully.

[ricardoasouz]

Hi! Just checking in on this PR. It looks like the workflows are still awaiting maintainer approval. Please let me know if there’s anything I should update or provide from my side. Thanks!

[mansnils]

Thank you @ricardoasouz !

[mansnils]

Thanks for the PR. Could you update date and versions in the updated files?
It should be a minor update - See README.md's 'Version & Date' section and https://semver.org/.

[ricardoasouz]

Thanks for the PR. Could you update date and versions in the updated files? It should be a minor update - See README.md's 'Version & Date' section and https://semver.org/.

Updated the date and minor versions in all three modified source files, and rebased onto the latest main. Thanks!