GCC PR 67968 provides a test case that causes a gccgo crash.  The
crash is because the compiler failed to build the hash and equality
functions required for a type descriptor.  The descriptor is for an
unnamed type that is being returned by a function imported from a
different package.  The unnamed type is being implicitly converted to
an interface type by a return statement.  The fix is to ensure that
the type of a call expression is always traversed.  Bootstrapped and
ran Go testsuite on x86_64-pc-linux-gnu.  Committed to mainline and 5
branch.

Test case sent out for the master testsuite as https://golang.org/cl/16532 .

Ian