Fixes to let Ford docs work

[mathomp4]

Description

This PR adds some fixes to the Ford control file to:

1. Use cpp instead of pcpp as pcpp has issues with MAPL (see pcpp cannot handle our code: What's the best path forward? Fortran-FOSS-Programmers/ford#600)
2. Fix up excludes to ignore warnings.

Related Issue

Motivation and Context

Let's the docs build

How Has This Been Tested?

Tested in CI on fork.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Trivial change (affects only documentation or cleanup)

Checklist:

• I have tested this change with a run of GEOSgcm (if non-trivial)
• I have added one of the required labels (0 diff, 0 diff trivial, 0 diff structural, non 0-diff)
• I have updated the CHANGELOG.md accordingly following the style of Keep a Changelog