cmd/compile/internal/pgo: fix hard-coded PGO sample data position
This patch detects at which index position profiling samples that have the value-type samples count are, instead of the previously hard-coded position of index 1. Runtime generated profiles always generate CPU profiling data with the 0 index being CPU nanoseconds, and samples count at index 1, which is why this previously hasn't come up.
Fixes #58292
Change-Id: Idde761d53b02259f3076c4e5dcb4a96a9d53df0e
GitHub-Last-Rev:
dabbf9f88c560286e150e9b136a27c3ac23c5ec1
GitHub-Pull-Request: golang/go#58294
Reviewed-on: https://go-review.googlesource.com/c/go/+/465135
Auto-Submit: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>