bionic: fix integer overflows in chk_malloc(), leak_malloc(), and leak_memalign()

The allocation size in chk_malloc(), leak_malloc(), and leak_memalign()
functions may be rounded up to a small value, leading to buffer overflows.
The code only runs in debugging mode.

This patch complements commit 6f04a0f4 (CVE-2009-0607).

Change-Id: Id899bcd2bcd2ea2205e5753c433390710032dc83
Signed-off-by: Xi Wang <xi.wang@gmail.com>