i also didnt find in on my pc and i am using XP maybe it requires the latest Platform SDK so you can try downloading it and install.
but there is a solution simply gain pointer to the function dynamically 
Code:
typedef BOOL (*pDebugActiveProcessStop)(DWORD);
HINSTANCE h = ::GetModuleHandle("kernel32.dll");
if ( h == 0 )
h = ::LoadLibrary("kernel32.dll");
if (h)
{
pDebugActiveProcessStop pDAPStop = NULL;
pDAPStop = (pDebugActiveProcessStop) ::GetProcAddress(h,"DebugActiveProcessStop");
if (pDAPStop)
{
// call the fucntion if we gain a pointer to it
pDAPStop(0);
}
::FreeLibrary(h);
}
if i helped dont forget to rate :-)
Cheers