[libc] Fix running benchmarks under msan/asan

asan/msan intercepts `aligned_malloc` and misbehave when the requested
alignment is greater than 512.
https://github.com/llvm/llvm-project/blob/b041b613e6fff713fc9ad6dbc73024286fb2fc93/compiler-rt/lib/asan/asan_allocator.cpp#L430-L431