go/build, cmd/go: update to match recent changes to gc

go/build, cmd/go: update to match recent changes to gc

    Several recent changes to the gc version of cmd/go improve the
    gofrontend support. These changes are partially copies of existing
    gofrontend differences, and partially new code. This CL makes the
    gofrontend match the upstream code.

    The changes included here come from:
        https://golang.org/cl/111575
        https://golang.org/cl/111595
        https://golang.org/cl/111635
        https://golang.org/cl/111636

    For the record, the following recent gc changes are based on code
    already present in the gofrontend repo:
        https://golang.org/cl/110915
        https://golang.org/cl/111615

    For the record, a gc change, partially based on earlier gofrontend
    work, also with new gc code, was already copied to gofrontend repo in
    CL 111099:
        https://golang.org/cl/111097

    This moves the generated list of standard library packages from
    cmd/go/internal/load to go/build.

    Reviewed-on: https://go-review.googlesource.com/112475

gotools/:
	* Makefile.am (check-go-tool): Don't copy zstdpkglist.go.
	* Makefile.in: Rebuild.

From-SVN: r260097