libgo/testsuite: ignore symbols with a leading dot in symtogo

libgo/testsuite: ignore symbols with a leading dot in symtogo

    On AIX, a function has two symbols, a text symbol (with a leading dot)
    and a data one (without it).
    As the tests must be run only once, only the data symbol can be used to
    retrieve the final go symbol. Therefore, all symbols beginning with a dot
    are ignored by symtogo.

    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/177837

From-SVN: r272666