tst-mmap.so: Fix mincore() stack and malloc tests

Linux requires mincore() addresses to be page aligned.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
runtime: Check that mincore() address is page aligned

Make mincore() error-path compatible with Linux by requiring 'addr' to
be page aligned.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>