Fix warnings raising with GCC 15

[foxtran]

Description

This PR fixes warnings which I observed during FMS compilation with GCC 15 on MacOS using CMake build system.
All detected warnings were fixed.

How Has This Been Tested?
Tested using compilation with GCC 15.1 (gcc + gfortran), MacOS 22.6.0, CMake 4.0.2. OpenMPI 5.0.5 & NetCDF 4.9.3 were found. Release build was used.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes