build: add intptr typedef for Plan 9
Revision
01810e5c68e9 added the following to src/pkg/runtime/stack.h:
StackPreempt = (uintptr)(intptr)0xffffade,
The typedef for intptr is defined in two places:
1. src/pkg/runtime/runtime.h for use by the runtime
2. include/u.h for use by the compilers and linkers
On Plan 9, we don't use include/u.h but instead augment the host's
u.h with extra typedefs. These are in include/plan9/GOARCH/u.h.
We forgot to add intptr. It didn't cause a problem until now since
that typedef was never used outside the runtime.
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/
10023043