Revert^2 "Use a current entry pointer instead of index for the method trace buffer"

This reverts commit 44b5204a81e9263a612af65f426e66395ae9426b.

Reason for revert: Relanding after fix for failures. The curr_entry
should use a register that isn't rax or rdx on x86 and x86_64.

Change-Id: I9e19eae72b93b4c49c619a1b58a892040d975e3e
8 files changed