compiler: split writing of equal and hash functions for types

compiler: split writing of equal and hash functions for types

    Separate the generation of type equality and hash functions, rather
    than doing them in a single operation.

    This is almost entirely a pure refactoring in preparation for
    generating hash functions only for types that are map keys.  The only
    change in generated code is that for types that are the size of
    numeric types, but not aligned like numeric types, such as [8]byte,
    now use standard hash functions.  They previously used special-purpose
    hash functions because they required special-purpose equal functions.

    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/212842

From-SVN: r279847