runtime: fix misaligned 64-bit atomic
Fixes #4869.
Fixes #5007.
Update #5005.
R=golang-dev, 0xe2.0x9a.0x9b, bradfitz
CC=golang-dev
https://golang.org/cl/7534044
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index 8ae6e6a..d9afd5b 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -483,6 +483,7 @@
bool wait; // if true, wait while all threads finish processing,
// otherwise parfor may return while other threads are still working
ParForThread *thr; // array of thread descriptors
+ uint32 pad; // to align ParForThread.pos for 64-bit atomic operations
// stats
uint64 nsteal;
uint64 nstealcnt;