Most of the functions in the compositor cryptomatte file are declared
with extern "C" linkage, which can cause symbol conflict even when
functions exist in separate namespaces. This is not actually necessary,
as the declaration of the few functions that require C linkage are
already declared as such in the header file, so this patch removes the
extern C scope from that file.
Differential Revision: https://developer.blender.org/D15656
Reviewed By: Clement Foucault
5689dda6f7