This updates the runtime to HEAD to keep it aligned and fixes some bugs.

http://llvm.org/viewvc/llvm-project?view=revision&revision=285454
fixes the crash on darwin related to unaligned data section (#17065).

http://llvm.org/viewvc/llvm-project?view=revision&revision=285451
enables core dumps by default (#16527).

http://llvm.org/viewvc/llvm-project?view=revision&revision=285455
adds a hook to obtain number of races reported so far (#15972).
Can now be obtained with:

//go:nosplit
func RaceReportCount() int {
	var n uint64
	racecall(&__tsan_report_count, uintptr(unsafe.Pointer(&n)), 0, 0, 0)
	return int(n)
}

Fixes #16527.
Fixes #17065.
Update #15972.

Change-Id: I8f869cb6275c9521a47303f3810a9965e9314357
Reviewed-on: https://go-review.googlesource.com/32160
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>