Fix setting of call graph node AutoFDO count

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).
3d9e6767939e9658260e2506e81ec32b37cba041 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.