Updates for intrusive_ptr refcounting

[ajtribick]

• Initialize the refcounts with 1
• Use memory orderings that match the implementation of shared_ptr refcounting in libc++/Windows STL

Latter also matches the example in Herb Sutter's atomic<> weapons talk (discussion starts at 1:19:51), should be a little better on ARM.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud