Since some spice C++ code is using code from common/, the C
functions need to be marked as such for the C++ compiler, otherwise
we'll get linkage issues.
Every place that does a regular malloc/calloc and aborts on failure
should use spice_malloc/spice_mallo0 instead, which is leaner and cleaner.
Allocations of dynamically sized arrays can use g_malloc_n or g_new etc
which correctly handle multiplication overflow if some of the arguments
are not trusted.
