cmd/compile: remove a false dependency for TZCNT
LZCNT/TZCNT on some Intel CPUs suffer from a false dependency on
the destination register.
The problem was mentioned in the GCC Ticket: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62011#c7
and fixed with https://gcc.gnu.org/viewcvs?rev=214112&root=gcc&view=rev
Change-Id: I8109e84f03ac85f221b06d3b913612b58320d151
Reviewed-on: https://go-review.googlesource.com/c/go/+/369019
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Alex Rakoczy <alex@golang.org>
Run-TryBot: Alex Rakoczy <alex@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>