issue with aligned_alloc on macOS 10.12 with clang 802.0.42 cannot find <malloc.h>

It seems that under /usr/include malloc.h is at /usr/include/malloc/malloc.h

I thought we could use stdlib.h instead, but after some reading I found that this has other issues.

Anyway the use case was to compile tensorflow r1.6 from tensorflow/contrib/cmake on macOS 10.12 with cland 802.0.42 and everything worked apart from gemmlowp so I thought I ought to let you know.