build: adjustments for move from src/pkg to src

This CL adjusts code referring to src/pkg to refer to src.

Immediately after submitting this CL, I will submit
a change doing 'hg mv src/pkg/* src'.
That change will be too large to review with Rietveld
but will contain only the 'hg mv'.

This CL will break the build.
The followup 'hg mv' will fix it.

For more about the move, see golang.org/s/go14nopkg.

LGTM=r
R=r
CC=golang-codereviews
https://codereview.appspot.com/134570043
build: move package sources from src/pkg to src

Preparation was in CL 134570043.
This CL contains only the effect of 'hg mv src/pkg/* src'.
For more about the move, see golang.org/s/go14nopkg.
build: more adjustments for move from src/pkg to src

These were missed in CL 134570043.

Fixes nacl, solaris builds.

TBR=r
CC=golang-codereviews
https://codereview.appspot.com/136320043
doc/go1.4.txt: src/pkg directory is gone.

CC=golang-codereviews
https://codereview.appspot.com/139310043
build: merge the great pkg/ rename into dev.power64

This also removes pkg/runtime/traceback_lr.c, which was ported
to Go in an earlier commit and then moved to
runtime/traceback.go.

Reviewer: rsc@golang.org
          rsc: LGTM