Bug#421220: Not a package bug, but one in the experimental compiler
Ben Hutchings pointed out to me that this is in fact not a bug in your
code but in the compiler. GCC shouldn't reject this code because it's
valid. According to Ben, "A redundant semi-colon after a member function
definition in the class declaration is allowed. In 9.2 [class.mem] the
grammar has "member-declaration: ... function-definition ;opt".
The good news is that this has been fixed in GCC in SVN, so it won't
be an issue with the next upload of the gcc-package anymore. If upstream
has not accepted the (harmless) patch, please remove it again from your
Debian package in the next upload and do not forward it upstream.
Apologies for wasting your time.