cmd/compile: replace -d=pgoinline with -d=pgodebug

cmd/compile: replace -d=pgoinline with -d=pgodebug

We will soon have PGO specialization. It doesn't make sense for the
debug flag to have inline in the name, so rename it to pgodebug.

pgoinline is now a flag that can be used to disable PGO inlining.
Devirtualization will have a similar debug flag.

For #59959.

Change-Id: I9770ff1f0d132dfa3cd417018a887a1bd5555bba
Reviewed-on: https://go-review.googlesource.com/c/go/+/494716
Auto-Submit: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>