[s1898] 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>

(based on commit [12365] - 772a5bb)

Signed-off-by: Xfurry <xfurry@scriptdev2.com>