Description
In this PR, #include fms_platform.h has been replaced with use platform_mod in several mpp unit tests. This is to avoid compilations when FMS is compiled with --enable-portable-kinds. See issue below for more details.

Fixes #1615

How Has This Been Tested?
Unit tests in test_fms/mpp pass with GCC 14 on the amdbox.

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