compiler: Don't built hash/equality functions for thunk structs.

compiler: Don't built hash/equality functions for thunk structs.

They are never necessary, and they can cause problems when a
thunk is used to pass an unexported type from a different
package to a function defined in that package.  The resulting
struct type may need to call the comparison routine from the
other package, which will fail because the type is not
exported.  This will be bug492 in the master testsuite.

From-SVN: r218798