toolchain_build: Update EXPAT library
toolchain_build: Update EXPAT library

This library goes into the GDB build.
It has a new upstream version with various fixes.

BUG= none
TEST= toolchain trybots
R=bradnelson@google.com, dyen@chromium.org

Review URL: https://codereview.chromium.org/256653002

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@13081 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client