Change ARM calls into indirect calls.

This is done by putting far pointers (for calls) into a
register and then do an indirect call.

This was done to guarantee that we aren't putting a size limit on ARM32 executables.

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4076
R=jpp@chromium.org

Review URL: https://codereview.chromium.org/1687553002 .