Replace custom alignment_of_long_double with alignof

[devreal]

alignof was standardized in C11 and OMPI now requires it.

[Copilot]

Pull request overview

This PR modernizes the codebase by replacing a custom alignment_of_long_double() helper function with the C11 standard alignof operator. The change removes legacy compatibility code now that the project requires C11.

Key changes:

• Removed the custom alignment_of_long_double() function (lines 484-507 removed)
• Updated two call sites to use alignof(long double) directly

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[Copilot]

The code uses alignof without including <stdalign.h>. In C11, alignof is a macro defined in <stdalign.h> that expands to _Alignof, while _Alignof is the actual keyword. For consistency with other parts of the codebase (see opal/include/opal/align.h line 33), and to avoid requiring <stdalign.h>, consider using _Alignof(long double) directly instead of alignof(long double).

Suggested change

	int alignment_mask = alignof(long double) - 1;
	int alignment_mask = _Alignof(long double) - 1;

[Copilot]

The code uses alignof without including <stdalign.h>. In C11, alignof is a macro defined in <stdalign.h> that expands to _Alignof, while _Alignof is the actual keyword. For consistency with other parts of the codebase (see opal/include/opal/align.h line 33), and to avoid requiring <stdalign.h>, consider using _Alignof(long double) directly instead of alignof(long double).

Suggested change

	int alignment_mask = alignof(long double) - 1;
	int alignment_mask = _Alignof(long double) - 1;

[bosilca]

I like copilot suggestion

[devreal]

Agreed, makes it clear that it's a language feature. Force-pushed a change.