There is a difference between GCC supplied by ARM and NXP's GCC build. In general, all our changes are documented in the 'patches_applied' folder of the GCC tools in Design Studio. Some of these changes may already be in the FSF repository, but some are certainly not. For example, there is a feature to change the scope of pragma section to be file scope. The work for this was a bit wonky and likely would never be accepted by the open-source community. Nonetheless, we supplied this feature in our NXP gcc builds. Additionally, we support more library configurations (multi-libs) than you would probably find in the ARM sourced toolchain. Additionally, ARM comments that:
Note: GCC sources are picked from an Arm vendor branch which is based on an official gcc release branch. Sometimes, patches are cherry-picked as needed to the Arm vendor branch for binary releases.
So, we didn't try to find out which patches are cherry-picked from the ARM vendor branch of the gcc release branches.
In general, you won't find much difference between the two compilers (for the same version), but the NXP compilers are used by our SDK teams, so they ensure NXP products work with the NXP source gcc release.
Hope this helps.