Fix issues in libunwindstack.

- Add a load_bias field in MapInfo so that it can be loaded offline,
  and also so it can be cached.
- Add an Add function to the Maps class so that it's possible to manually
  create a map.
- Remove the OfflineMaps class since I haven't found a reason for this to
  exist.
- Add a pointer to the gnu debugdata compressed section in the interface
  itself and modify the step path to try eh_frame, then debug_frame, then
  gnu_debugdata. This way arm can add exidx as the last step behind
  gnu_debugdata. Add an offline test to verify the order of unwind.
- Fix x86_64_ucontext_t since it was a different size on 32 bit and 64 bit
  systems.

Test: Pass new unit tests.
Change-Id: I978b70d6c244bd307c62a29886d24c1a8cb2af23
diff --git a/libunwindstack/Android.bp b/libunwindstack/Android.bp
index 21dd306..5e94388 100644
--- a/libunwindstack/Android.bp
+++ b/libunwindstack/Android.bp
@@ -167,6 +167,7 @@
     data: [
         "tests/files/elf32.xz",
         "tests/files/elf64.xz",
+        "tests/files/offline/gnu_debugdata_arm32/*",
         "tests/files/offline/straddle_arm32/*",
         "tests/files/offline/straddle_arm64/*",
     ],