Remove <malloc.h> from the system.

Remove <malloc.h> from the system.

Originally, I wanted to follow FreeBSD which errors if __STDC__ is
defined and silently includes <stdlib.h>, which has the malloc()
and friends prototypes, if it is not defined. The only case where
__STDC__ isn't defined used to be when -traditional was passed to
GCC, which used to attempt an emulation of a pre-standard compiler.
But -traditional has since been made a cpp(1) specific option in
newer releases of GCC, so it becomes more and more pointless to
support <malloc.h>, even if we went with FreeBSD's version.

Therefore, remove it completely.

Also disable its usage in a number of contrib/ software which
expected it due to its presence at the time when the software was
configured.

Suggested-by: marino, who also fixed the resultant dports breakage