Fix setting of call graph node AutoFDO count

We are initializing both the call graph node count and
the entry block count of the function with the head_count value
from the profile.

Count propagation algorithm may refine the entry block count
and we may end up with a case where the call graph node count
is set to zero but the entry block count is non-zero. That becomes
a problem because we have this code in execute_fixup_cfg:

 profile_count num = node->count;
 profile_count den = ENTRY_BLOCK_PTR_FOR_FN (cfun)->count;
 bool scale = num.initialized_p () && !(num == den);

Here if num is 0 but den is not 0, scale becomes true and we
lose the counts in

if (scale)
  bb->count = bb->count.apply_scale (num, den);

This is what happened in the issue reported in PR116743
(a 10% regression in MySQL HAMMERDB tests).
3d9e6767 made an improvement in
AutoFDO count propagation, which caused a mismatch between
the call graph node count (zero) and the entry block count (non-zero)
and subsequent loss of counts as described above.

The fix is to update the call graph node count once we've done count propagation.

Tested on x86_64-pc-linux-gnu.

gcc/ChangeLog:
	PR gcov-profile/116743
	* auto-profile.cc (afdo_annotate_cfg): Fix mismatch between the call graph node count
	and the entry block count.