What version of MCUXpresso IDE are you using? v11.0.0 provides a fix for this issue:
Fixed issue with IDE losing C library include paths. This did not prevent projects from building but meant that indexer-related functionality reliant on these paths would not work correctly (for instance trying to open a C library include file from the editor). This issue could also cause Newlib projects to sometimes appear to be using Redlib include files.
Note: Existing projects can be "fixed" using Tools->Fixup Parsers option on the Project Properties view's context sensitive menu
MCUXpresso IDE Support
this is what helped for my projects:
1) right-click on the project and use Tools > Fixup Parsers
2) checking the Paths and Symbols for the project and removing any references to the IDE or previous IDE installation:
3) Checking that there is an 'MCU GCC Built-In Compiler parser' present pointing to the Include folders in the IDE:
4) Doing a Index rebuild on the project:
I hope this helps,
This is what I had: I selected the item pointing to 10.3.1 and used the 'Delete' button.
This is not possible for you (you did not share the state of the button)? Or what do you get (error message?).