ggml-base: use MATH_LIBRARY variable instead of hardcoded 'm' (llama/22239)

Fixes #22237 — the find_library(MATH_LIBRARY m) result was being
discarded and the target linked against the literal 'm' string.

This prevents users from overriding the math library (e.g. for AMD AOCL)
via CMake variables. Now the discovered MATH_LIBRARY is used directly.

ggml/src/CMakeLists.txt

@@ -473,7 +473,7 @@ target_link_libraries(ggml-base PRIVATE Threads::Threads)
 find_library(MATH_LIBRARY m)
 if (MATH_LIBRARY)
     if (NOT WIN32 OR NOT DEFINED ENV{ONEAPI_ROOT})
-        target_link_libraries(ggml-base PRIVATE m)
+        target_link_libraries(ggml-base PRIVATE ${MATH_LIBRARY})
     endif()
 endif()