malloc.h: be a bit more consistent with macro definitions

malloc.h: be a bit more consistent with macro definitions

Currrently, malloc and free are function-like macros, while calloc,
realloc and memalign are object-like macros.

Usually, this doesn't matter, but it does when the identifiers appear
without a following open parenthesis, such as when their address is
taken for building the export table. Adding calloc or realloc to that
table breaks the build on sandbox due to this inconsistency.

Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>
Reviewed-by: Tom Rini <trini@konsulko.com>