Move large structure off the stack.

The struct unw_addr_space is very large (at least 13624 bytes on arm),
but is on the stack in the function map_create_list.

Allocate this function when needed instead of putting it on the stack.

Bug: 33293182

Test: Built and ran backtrace_test on an angler. Stepped through the
Test: modified code and verified it is called and allocated properly.
Test: Ran valgrind on the backtrace_test.local_trace to verify that
Test: the memory is not leaked.
Change-Id: I298e72d6b87d2701111c4659c46246b308f275e9
(cherry picked from commit 50270d3e)