Switches the instruction counting inlined code for AArch64 drmemtrace's delayed-by-instruction-count feature to count down and use TBZ, avoiding use of the arithmetic flags.
Adds INSTR_CREATE_ support for TBZ and TBNZ.
Fixes missing support for subtracting in drx_insert_counter_update() for AArch64 (fatal encoder errors are raised without this). Adds a drx test for subtracting.
Issue: #5026 (closed)