[CUDA] Fix false-positive in known-emitted handling.

Previously: When compiling for host, our constructed call graph went
*through* kernel calls.  This meant that if we had

  host calls kernel calls HD

we would incorrectly mark the HD function as known-emitted on the host
side, and thus perform host-side checks on it.

Fixing this exposed another issue, wherein when marking a function as
known-emitted, we also need to traverse the callgraph of its template,
because non-dependent calls are attached to a function's template, not
its instantiation.

llvm-svn: 284355