ggml-cpu : disable tiled matmul on AIX to fix page boundary segfault (llama/22293)

ggml-cpu : disable tiled matmul on AIX to fix page boundary segfault (llama/22293)

* ggml-cpu : disable tiled matmul on AIX to fix page boundary segfault

vec_xst operations in the tiled path crash on AIX when writing
near 4KB page boundaries due to strict memory protection. Fall
back to mnpack implementation on AIX for stable execution.

Signed-off-by: Shalini Salomi Bodapati <redacted>
* Update ggml/src/ggml-cpu/llamafile/sgemm.cpp

Co-authored-by: Aaron Teo <redacted>
* Update sgemm.cpp

* Update sgemm.cpp

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Signed-off-by: Shalini Salomi Bodapati <redacted>
Co-authored-by: Aaron Teo <redacted>