Libunwind: Fix unused value

For build-system CFLAGS clean-up, "fix" unused value:

For recent compilers, e.g., GCC 4.9 used for aarch64, the ", 0" in
the macro will be recognized as an unused value. However, the zero
is required in other places of the code, so can't be removed.

Bug: 18632512
Change-Id: I96054c368e04e77988e26c567ad324a33a3cf839
1 file changed