undo CL 138250043 / 4eda5e4001fd

I will use different approach to solve this problem.
See CL 143160046 for details.

««« original CL description
syscall: keep Windows syscall pointers live too

Like https://codereview.appspot.com/139360044

LGTM=rsc, alex.brainman
R=alex.brainman, rsc
CC=golang-codereviews
https://codereview.appspot.com/138250043
»»»

LGTM=r
R=golang-codereviews, bradfitz, r
CC=golang-codereviews
https://codereview.appspot.com/147440043