gotest: multiple +build lines must all be true

gotest: multiple +build lines must all be true

    The code that handled +build lines did not correctly require them to all
    be true.  While looking into this I discovered that multiple +build
    lines were mishandled in a different way, because the shell does not
    preseve line breaks in backquoted data.  Look for the +build token to
    tell us when we are switching from one +build line to another.

    Reviewed-on: https://go-review.googlesource.com/25460

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@239100 138bc75d-0d04-0410-961f-82ee72b054a4