sync_posix: Add Linux-specific monotonic clock preference
sync_posix: Add Linux-specific monotonic clock preference

When gRPC is running during wall clock acquisition, it's useful
to avoid wall clock references as much as possible.

sreecha/grpc,Vizerai/grpc,geffzhang/grpc,deepaklukose/grpc,chrisdunelm/grpc,simonkuang/grpc,deepaklukose/grpc,deepaklukose/grpc,donnadionne/grpc,donnadionne/grpc,muxi/grpc,deepaklukose/grpc,firebase/grpc,muxi/grpc,murgatroid99/grpc,sreecha/grpc,ncteisen/grpc,muxi/grpc,pszemus/grpc,geffzhang/grpc,mehrdada/grpc,firebase/grpc,sreecha/grpc,firebase/grpc,ctiller/grpc,jtattermusch/grpc,jboeuf/grpc,ejona86/grpc,sreecha/grpc,kpayson64/grpc,ctiller/grpc,ejona86/grpc,ctiller/grpc,kpayson64/grpc,ncteisen/grpc,ctiller/grpc,pszemus/grpc,sreecha/grpc,firebase/grpc,deepaklukose/grpc,firebase/grpc,ctiller/grpc,murgatroid99/grpc,ncteisen/grpc,kpayson64/grpc,stanley-cheung/grpc,stanley-cheung/grpc,chrisdunelm/grpc,ncteisen/grpc,kpayson64/grpc,donnadionne/grpc,vjpai/grpc,thinkerou/grpc,grpc/grpc,murgatroid99/grpc,firebase/grpc,simonkuang/grpc,carl-mastrangelo/grpc,jtattermusch/grpc,firebase/grpc,muxi/grpc,ctiller/grpc,jboeuf/grpc,stanley-cheung/grpc,mehrdada/grpc,kpayson64/grpc,firebase/grpc,kpayson64/grpc,jtattermusch/grpc,grpc/grpc,mehrdada/grpc,carl-mastrangelo/grpc,muxi/grpc,donnadionne/grpc,sreecha/grpc,stanley-cheung/grpc,mehrdada/grpc,jtattermusch/grpc,firebase/grpc,ncteisen/grpc,ctiller/grpc,jtattermusch/grpc,stanley-cheung/grpc,donnadionne/grpc,Vizerai/grpc,sreecha/grpc,ncteisen/grpc,vjpai/grpc,ejona86/grpc,ctiller/grpc,stanley-cheung/grpc,pszemus/grpc,ejona86/grpc,ncteisen/grpc,simonkuang/grpc,geffzhang/grpc,donnadionne/grpc,donnadionne/grpc,grpc/grpc,grpc/grpc,mehrdada/grpc,grpc/grpc,vjpai/grpc,ncteisen/grpc,thinkerou/grpc,pszemus/grpc,thinkerou/grpc,Vizerai/grpc,jtattermusch/grpc,Vizerai/grpc,deepaklukose/grpc,stanley-cheung/grpc,nicolasnoble/grpc,geffzhang/grpc,muxi/grpc,thinkerou/grpc,jboeuf/grpc,ejona86/grpc,ctiller/grpc,thinkerou/grpc,ncteisen/grpc,jtattermusch/grpc,jboeuf/grpc,ejona86/grpc,deepaklukose/grpc,carl-mastrangelo/grpc,muxi/grpc,firebase/grpc,grpc/grpc,grpc/grpc,ctiller/grpc,vjpai/grpc,geffzhang/grpc,vjpai/grpc,jboeuf/grpc,pszemus/grpc,carl-mastrangelo/grpc,Vizerai/grpc,kpayson64/grpc,donnadionne/grpc,geffzhang/grpc,geffzhang/grpc,chrisdunelm/grpc,nicolasnoble/grpc,chrisdunelm/grpc,simonkuang/grpc,stanley-cheung/grpc,mehrdada/grpc,pszemus/grpc,muxi/grpc,grpc/grpc,nicolasnoble/grpc,chrisdunelm/grpc,kpayson64/grpc,thinkerou/grpc,dgquintas/grpc,chrisdunelm/grpc,sreecha/grpc,kpayson64/grpc,murgatroid99/grpc,geffzhang/grpc,mehrdada/grpc,pszemus/grpc,pszemus/grpc,sreecha/grpc,vjpai/grpc,muxi/grpc,stanley-cheung/grpc,jtattermusch/grpc,ejona86/grpc,ncteisen/grpc,Vizerai/grpc,simonkuang/grpc,ejona86/grpc,mehrdada/grpc,grpc/grpc,simonkuang/grpc,Vizerai/grpc,simonkuang/grpc,jboeuf/grpc,carl-mastrangelo/grpc,grpc/grpc,stanley-cheung/grpc,ejona86/grpc,murgatroid99/grpc,pszemus/grpc,jtattermusch/grpc,dgquintas/grpc,deepaklukose/grpc,nicolasnoble/grpc,mehrdada/grpc,carl-mastrangelo/grpc,nicolasnoble/grpc,chrisdunelm/grpc,thinkerou/grpc,carl-mastrangelo/grpc,dgquintas/grpc,nicolasnoble/grpc,donnadionne/grpc,grpc/grpc,carl-mastrangelo/grpc,simonkuang/grpc,nicolasnoble/grpc,vjpai/grpc,nicolasnoble/grpc,nicolasnoble/grpc,jtattermusch/grpc,nicolasnoble/grpc,dgquintas/grpc,jboeuf/grpc,carl-mastrangelo/grpc,murgatroid99/grpc,chrisdunelm/grpc,dgquintas/grpc,carl-mastrangelo/grpc,donnadionne/grpc,thinkerou/grpc,mehrdada/grpc,thinkerou/grpc,Vizerai/grpc,sreecha/grpc,mehrdada/grpc,ncteisen/grpc,carl-mastrangelo/grpc,muxi/grpc,firebase/grpc,jboeuf/grpc,grpc/grpc,donnadionne/grpc,ncteisen/grpc,ejona86/grpc,dgquintas/grpc,sreecha/grpc,jboeuf/grpc,pszemus/grpc,dgquintas/grpc,simonkuang/grpc,dgquintas/grpc,pszemus/grpc,murgatroid99/grpc,chrisdunelm/grpc,vjpai/grpc,ejona86/grpc,dgquintas/grpc,Vizerai/grpc,jboeuf/grpc,ctiller/grpc,chrisdunelm/grpc,dgquintas/grpc,kpayson64/grpc,thinkerou/grpc,geffzhang/grpc,firebase/grpc,vjpai/grpc,chrisdunelm/grpc,donnadionne/grpc,jboeuf/grpc,vjpai/grpc,vjpai/grpc,thinkerou/grpc,mehrdada/grpc,Vizerai/grpc,carl-mastrangelo/grpc,sreecha/grpc,ctiller/grpc,stanley-cheung/grpc,muxi/grpc,deepaklukose/grpc,dgquintas/grpc,stanley-cheung/grpc,murgatroid99/grpc,murgatroid99/grpc,vjpai/grpc,nicolasnoble/grpc,thinkerou/grpc,kpayson64/grpc,jtattermusch/grpc,Vizerai/grpc,ejona86/grpc,jtattermusch/grpc,pszemus/grpc,muxi/grpc,jboeuf/grpc,nicolasnoble/grpc,murgatroid99/grpc