cmd/compilebench: generate separate cpu profiles when using -count
cmd/compilebench: generate separate cpu profiles when using -count

When the -count flag is provided,
instead of having each run overwrite the previous profile,
add a count suffix to the profile filename.
Then you can combine the profiles with

go tool pprof `go tool -n compile` <all profile files here>

This allows generation of precise profiles,
even for fast-compiling packages.

Change-Id: I006cf8fad143346b28a646a0b3582cc0f6eec310
Reviewed-on: https://go-review.googlesource.com/39718
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>

syreclabs/go-tools,golang/tools,syreclabs/go-tools,golang/tools,syreclabs/go-tools,golang/tools,syreclabs/go-tools,golang/tools,syreclabs/go-tools,golang/tools,syreclabs/go-tools