Fix fatal crash on 64 bit Linux

Fix fatal crash on 64 bit Linux

By default, OpenJPEG uses the function memalign to allocate aligned
memory on Linux systems. That function needs malloc.h which was
missing. This results in a compiler warning:

openjpeg/src/lib/openjp2/opj_malloc.c:63:3: warning:
 implicit declaration of function ‘memalign’
 [-Wimplicit-function-declaration]

On hosts where sizeof(int) < sizeof(void *) the return value of memalign
will be truncated which results in an invalid pointer.

That caused "make test" to produce lots of segmentation faults when
running on a 64 bit Linux host.

Signed-off-by: Stefan Weil <sw@weilnetz.de>