The parser in package gccgoimporter does not seem to handle type conversion expressions exported by gccgo. For example, the following constant:

type Units string

const Bits = Units("bits")

gets exported by gccgo in a .gox file as a const value wrapped in a type conversion:

const Bits <type 1 "Units" <type -16>> = convert(<type 1>, "bits");

When gccgoimporter tries to parse this const in gccgoimporter.(*parser).parseConstValue, it appears to only expect a constant string, literal, int, or float on the RHS of a const assignment, so we get the error:

import error some/package/path:48:49 (byte offset = 10429): expected const value,
got Ident ("convert"))

The importer in the gccgo frontend, however, handles this type conversion properly (see relevant source snippet here).