api/core: annotate structs/functions for C linkage
Annotate as extern "C" when included in C++ files to prevent issues due
to conflicting linkage - C vs C++. With follow up commits we'll remove
the "extern "C" { #include "header.h" } pattern which we currently use.
Conditionally including system headers (either directly or not) in such
a construct in a bad idea as they might include C++ symbols.
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>