Fix the stack/ tool for 64 bit archs.

pc values might now be 16 bytes wide. Also add support
for the arm64 architecture switch.

Change-Id: Ia2e0282f3bee03ef6092de285b0c32fa6da07cb0
Add android-20 bionic headers/symbols for 32-bit

Note that this is for bionic headers to be consistent with 64-bit
headers tentatively placed at android-20. ie.

1. bionic headers in all the existing 32-bit headers android-3 .. 19
   are consistent, and don't track any new development in bionic/
   since JB (the time when significant refactoring work starts in bionic/)
   unless bug fixes.
2. bionic headers in android-20 tracks bionic/

Change-Id: Ia07f04ac03ffaef6a6ddcea5f0e6b891e21a869a
Merge "Fix the stack/ tool for 64 bit archs."
Merge "Add android-20 bionic headers/symbols for 32-bit"
auto-merger: merge in from aosp/master