Fix unwind in exec maps with non-zero offsets.

The packed relocations have a non-zero load base, so libunwind needs
to account for that.

Bug: 20687795

(cherry picked from commit 517b197b9b49fdf65bd9ad8baa66cb374faad997)

Change-Id: I284ad94930b982136f8869d1633b29e5d6960ee7
7 files changed