Add a way to disable backtracing in malloc debug.

The property libc.debug.malloc.nobacktrace set to non-zero disables
getting backtracing when using mode 1 or mode 10.

Bug: 16874447

(cherry picked from 49de01a5be7bfb07baaea7415647d838383e1b59)

Change-Id: I6bbefe5420b14991fe84c2f849222dcd7cb592bf
3 files changed