Did you ask on the developers list?
Not yet, I still hope that @PascalDragon will see this question.
Thanks to @julkas, I saw a topic two years old, which states:
Yes and no. Yes: As of now for all targets FPC supports global variables (and static variables) are initialized to 0, but that is not guaranteed by the compiler, but by the OS, so if the OS decides not to do it then it won't be! That is also why we do not document this (thus the No).
However, current documentation states:
...
Remark
2 exceptions to this rule exist:
1. Managed types are an exception to this rule: Managed types are always initialized with a default value: in general this means setting the reference count to zero, or
setting the pointer value of the type to Nil. See section 3.9, page 223
2. Global variables are initialized with the equivalent of zero.