compiler: add COMPARE_ALIASES flag for type compare and hash

Normally aliases compare as identical to the underlying type.  Add a
COMPARE_ALIASES flag to let them compare (and hash) differently.  This
will be used by later patches in this series.

Change-Id: I75b0f65d9be19b7adf77bead276f37cd3984d40d
Reviewed-on: https://go-review.googlesource.com/c/143021
Reviewed-by: Than McIntosh <thanm@google.com>
2 files changed