Converts a string GUID into its binary encoding.
All string GUIDs are formatted as big endian but on-disk can be encoded in different ways.
| guidstr |
a GUID, e.g. `00112233-4455-6677-8899-aabbccddeeff` |
| guid |
a _guid_t, or NULL to just check the GUID |
| flags |
GUID flags, e.g. fwupd_guid_flag_mixed_endian |
|
true for success |