[12365] fix Singleton compile error on clang

some members of Singleton were implicitly specialized in the static function
definitions, which conflicted with the initialization of said members (clang
saw it as a redefinition of the specialization)

Signed-off-by: DasBlub <DasBlub@gmail.com>
[12366] fix clang compile error from implicit type conversion

Signed-off-by: DasBlub <DasBlub@gmail.com>
[12367] fix clang compile error from call of templated member function

Signed-off-by: DasBlub <DasBlub@gmail.com>