libreplace: Only check for malloc.h if needed

libreplace: Only check for malloc.h if needed

OpenBSD complains that malloc.h is deprecated on every gcc invocation.
That hides a lot of real warnings. malloc and friends nowadays are
typically defined in stdlib.h, only check there.

We need memalign. On OpenBSD this does not exist, so libreplace replaces
it. The wscript test in libreplace only checks whether memalign can
link. Unfortunately in glibc memalign comes from malloc.h.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>