Fix another set of bugs.

- The pc read from the eh frame binary table of pc/fde offset is off by 4.
  I verified that on arm/arm64/x86/x86_64 the pc in this table matches
  the fde pc_start value. I did this by adding an error if this occurred
  and ran unwind_info over everything in system/lib, system/lib64, system/bin.
- Fixed unit tests for the above change.
- Fix a small bug in the processing encoded values. The high
  bit of the encoding should be masked off, but I wasn't doing that. That
  meant during processing of the fde, I was incorrectly returning
  an error because the encoded value was unknown.
- Added a new test for this encoding change.

Bug: 23762183

Test: Build and all unit tests pass. Also, see above comments.
Change-Id: If074a410a1726392274cd72c64470ca0be48e0db