Sysmon can actually get the RW lock execLock while holding the sysmon
lock (if no M is available), so there is an edge from lockRankSysmon to
lockRankRwmutexR. The stack trace is sysmon() [gets sched.sysmonlock] ->
startm() -> newm() -> newm1() -> execLock.runlock() [gets
execLock.rLock]
Change-Id: I9658659ba3899afb5219114d66b989abd50540db
Reviewed-on: https://go-review.googlesource.com/c/go/+/265721
Trust: Dan Scales <danscales@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com>