devel/edb: unbreak build with Clang 6 (C++14 by default)

os/unix/freebsd/MemoryRegions.cpp:99:9: error: no matching function for call to 'ptrace'

while(ptrace(PT_VM_ENTRY, pid_, reinterpret_cast<char*>(&vm_entry), NULL) == 0) {
      ^~~~~~

/usr/include/sys/ptrace.h:218:5: note: candidate function not viable: no known conversion from 'nullptr_t' to 'int' for 4th argument
int ptrace(int _request, pid_t _pid, caddr_t _addr, int _data);

^

Reported by: pkg-fallout