Unused variable from heap alloc code

[anthonyalayo]

Hey there,

I'm seeing the following warning on AppleClang:

src/alloc-aligned.c:162:14: warning: unused variable '_mi_heap_malloc_aligned' [-Wunused-variable]

I tried to pass in some CMAKE_CXX_FLAGS to fix it myself, but it looks like that doesn't work based on how the code was written.