ggml-cpu : disable tiled matmul on AIX to fix page boundary segfault (#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 <Shalini.Salomi.Bodapati@ibm.com>

* Update ggml/src/ggml-cpu/llamafile/sgemm.cpp

Co-authored-by: Aaron Teo <taronaeo@gmail.com>

* Update sgemm.cpp

* Update sgemm.cpp

---------

Signed-off-by: Shalini Salomi Bodapati <Shalini.Salomi.Bodapati@ibm.com>
Co-authored-by: Aaron Teo <taronaeo@gmail.com>

Author: shalinib-ibm

ggml/src/ggml-cpu/llamafile/sgemm.cpp

@@ -2321,6 +2321,9 @@ class tinyBLAS_Q0_PPC {
     }
 
     void matmul(int64_t m, int64_t n) {
+    #if defined(_AIX) || defined(__BIG_ENDIAN__)
+        mnpack(0, m, 0, n);
+    #else
         const int64_t mc = 64;
         const int64_t kc = 64;
         int64_t nc = 64;
@@ -2334,7 +2337,6 @@ class tinyBLAS_Q0_PPC {
         } else {
             n_aligned = (n / 64) * 64;
         }
-
         if (n_aligned > 0) {
             if (n_aligned % 64 == 0)      nc = 64;
             else if (n_aligned == n)      nc = n;
@@ -2352,6 +2354,7 @@ class tinyBLAS_Q0_PPC {
         } else {
             mnpack(0, m, 0, n);
         }
+    #endif
     }
 
   private:
@@ -3191,12 +3194,16 @@ class tinyBLAS_PPC {
     }
 
     void matmul(int64_t m, int64_t n) {
+    #if defined(_AIX) || defined(__BIG_ENDIAN__)
+        mnpack(0, m, 0, n);
+    #else
         int64_t mc = 256; int64_t nc = 256; int64_t kc = 256;
         if (m % mc == 0 && n % nc == 0 && k % kc == 0) {
             matmul_tiled(m, n, mc, nc, kc);
         } else {
             mnpack(0, m, 0, n);
         }
+    #endif
     }
 
   private: