The CL 49090043 renamed Ureg structures to Ureg386,
UregArm and UregAmd64. This broke build on Plan 9,
since ureg_x86.h includes /386/include/ureg.h, which
declares a structure named Ureg instead of Ureg386.
R=golang-codereviews, bradfitz
CC=golang-codereviews, rsc
https://golang.org/cl/49260043
Previously, I had made available a tarball of
the modified system headers that were necessary
to build on Plan 9 but that was only a stopgap.
I think this method is much better since no
files outside of $GOROOT will have to be added
or modified during the build process.
Also, this is just the first step. I'll change
the build to reference these files in another CL
(that also contains a few more Makefile changes).
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5552056
