SWDEV-573004 - fix shfl_sync for compiler init value

[shadidashmiz]

• Add maybe undef attribute to shfl synch to avoid compiler failure of un initialized value

Motivation

Make shfl sync compatible with cuda

Technical Details

Add the attribute to make the shfl sync work with uninitialized variables.

JIRA ID

SWDEV-573004

Test Plan

Hip tests

Test Result

PSDB test results

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.

[Copilot]

Pull request overview

This PR adds the MAYBE_UNDEF attribute to the var parameter in all four shfl_sync function variants (__shfl_sync, __shfl_up_sync, __shfl_down_sync, and __shfl_xor_sync) to fix compiler initialization value handling. The maybe_undef attribute indicates to the compiler that it's acceptable for these parameters to be uninitialized, which is appropriate for warp shuffle operations where lanes may use values from other lanes.

Key changes:

• Added MAYBE_UNDEF attribute to the var parameter in all four template shfl_sync functions
• Changes align with the pattern already used in non-sync warp functions in amd_warp_functions.h

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