CMake check system for underscore requirements between C and Fortran

[islas]

TYPE: enhancement

KEYWORDS: cmake, configuration

SOURCE: internal

DESCRIPTION OF CHANGES:
Problem:
The current solution for implicitly matching symbols between C and Fortran relies on user-modification of a stanza for their system. While stanzas can be configured to a specific architecture and options selection, this approach is limited and overly specific to user configuration when it could be programmatically determined. Likewise, if a new stanza is introduced it will likely only be tested by one user on their particular system. Thus, if this stanza could be used elsewhere but needs underscores on C symbols for Fortran usage it will not be evident why the stanza does not work for this new user.

Solution:
Programmatically determine if underscores are needed in C compilation in the CMake build. Sanitize out any definition of underscore in the stanza so that CMake configuration checks take precedence.

[islas]

Requires #2056, #2053, #2086, #2087, #2088, and #2090

[islas]

@amstokely @mgduda This is ready to be reviewed again. The plan is to get this and its dependent PRs into the upcoming release. Thanks!

[Copilot]

Pull Request Overview

This PR introduces a CMake-based system to programmatically determine whether underscores are needed when linking C and Fortran code, replacing the previous manual stanza-based configuration approach. This eliminates platform-specific configuration errors and makes the build system more portable.

Key Changes:

• Adds compile/link tests to automatically detect C-Fortran symbol naming conventions
• Removes hardcoded underscore definitions from architecture configuration files
• Applies the detected underscore requirements as compile definitions across the project

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
confcheck/check_underscore.f90	Test program that calls a C function from Fortran to verify symbol compatibility
confcheck/check_underscore.c	C implementation that conditionally adds underscores based on preprocessor definitions
confcheck/CMakeLists.txt	Configuration checks that test both NOUNDERSCORE and UNDERSCORE symbol conventions
cmake/confcheck.cmake	Minor improvements to check result handling and error messaging
arch/configure_reader.py	Sanitization logic to strip underscore definitions from legacy stanzas
CMakeLists.txt	Applies the detected underscore convention as a compile definition

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[Copilot]

Corrected spelling of 'needing' to 'needed' and 'intrefacing' to 'interfacing'.

Suggested change

	# Check if underscores are needing for implicit c-Fortran intrefacing functions that
	# Check if underscores are needed for implicit c-Fortran interfacing functions that

[Copilot]

Corrected spelling of 'incease' to 'increase'.

Suggested change

	# so we won't use it here until we see reasonable need to incease the
	# so we won't use it here until we see reasonable need to increase the

[Copilot]

The check uses #ifdef UNDERSCORE but the CMake configuration defines -DUNDERSCORE which sets it to a value. Consider using #if defined(UNDERSCORE) or checking if the define should be set without a value (e.g., just -DUNDERSCORE without =1).

Suggested change

	#ifdef UNDERSCORE
	#if defined(UNDERSCORE)