compiler: revise exportdata fix for processing constant types

compiler: revise exportdata fix for processing constant types

    This patch is an addendum to the fix for issue 34577, which was not
    sufficiently general. During export data processing, when looking at
    the types of constants mentioned in inlinable function bodies, include
    both locally defined constants and constant imported from other
    packages.

    Testcase for this bug is in CL 201017.

    Fixes golang/go#34852.

    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/201018

From-SVN: r276976