ggml-cpu: fix uncaught underscore terminators for s390x

[taronaeo]

This pull request fixes unterminated underscores with __attribute__ in the s390x codebase.

Verification

To ensure that this patch did not break anything, the patch has been tested on the following models:

1. Tested IBM Granite 3.1 (F16)

Note

Tests were conducted on an IBM z15 Mainframe with 16 IFLs (cores) and 160 GB Memory on an LPAR.

[Copilot]

Pull Request Overview

This PR fixes unterminated __attribute__ usages in S390x vector typedefs and aligns spacing for consistency.

• Adds missing underscores around __attribute__((vector_size(16))) for double64x2_t and long64x2_t.
• Adjusts whitespace in typedef declarations to match surrounding lines.

Comments suppressed due to low confidence (2)

ggml/src/ggml-cpu/ggml-cpu-impl.h:386

• [nitpick] Consider adding an extra space before __attribute__ to align with other typedefs (e.g., two spaces) for consistent formatting.

typedef double double64x2_t __attribute__((vector_size(16)));

ggml/src/ggml-cpu/ggml-cpu-impl.h:388

• [nitpick] The spacing between signed and long appears irregular; using single spaces and aligning with other lines could improve readability.

typedef signed   long long long64x2_t  __attribute__((vector_size(16)));