re PR go/80302 (FAIL: time on systems with tzdata2017b installed)

re PR go/80302 (FAIL: time on systems with tzdata2017b installed)

	PR go/80302
    time: make the ParseInLocation test more robust

    This is a backport of https://golang.org/cl/37964 from the gc toolchain.

    Original description:

        The tzdata 2017a update (2017-02-28) changed the abbreviation of the
        Asia/Baghdad time zone (used in TestParseInLocation) from 'AST' to the
        numeric '+03'.

        Update the test so that it skips the checks if we're using a recent
        tzdata release.

    Updates golang/go#19457
    Fixes GCC PR 80302.

    Reviewed-on: https://go-review.googlesource.com/39470

From-SVN: r246695