Fix fetching CXX variable in setup.py (#28873)
Fix fetching CXX variable in setup.py (#28873)

* Fix fetching CXX variable in setup.py

* Preserve all elements of CXX variable in setup.py
vjpai/grpc,ejona86/grpc,jtattermusch/grpc,ejona86/grpc,ejona86/grpc,jtattermusch/grpc,stanley-cheung/grpc,vjpai/grpc,vjpai/grpc,stanley-cheung/grpc,ejona86/grpc,nicolasnoble/grpc,jtattermusch/grpc,nicolasnoble/grpc,vjpai/grpc,grpc/grpc,nicolasnoble/grpc,ctiller/grpc,ctiller/grpc,jtattermusch/grpc,grpc/grpc,stanley-cheung/grpc,nicolasnoble/grpc,ctiller/grpc,nicolasnoble/grpc,grpc/grpc,grpc/grpc,jtattermusch/grpc,grpc/grpc,grpc/grpc,nicolasnoble/grpc,stanley-cheung/grpc,grpc/grpc,vjpai/grpc,ctiller/grpc,ctiller/grpc,ctiller/grpc,nicolasnoble/grpc,ctiller/grpc,stanley-cheung/grpc,nicolasnoble/grpc,grpc/grpc,ctiller/grpc,jtattermusch/grpc,nicolasnoble/grpc,ejona86/grpc,vjpai/grpc,ctiller/grpc,stanley-cheung/grpc,jtattermusch/grpc,vjpai/grpc,nicolasnoble/grpc,grpc/grpc,nicolasnoble/grpc,jtattermusch/grpc,ejona86/grpc,stanley-cheung/grpc,jtattermusch/grpc,ejona86/grpc,stanley-cheung/grpc,vjpai/grpc,ctiller/grpc,stanley-cheung/grpc,stanley-cheung/grpc,grpc/grpc,ejona86/grpc,ctiller/grpc,ejona86/grpc,jtattermusch/grpc,grpc/grpc,ejona86/grpc,grpc/grpc,ejona86/grpc,jtattermusch/grpc,stanley-cheung/grpc,stanley-cheung/grpc,jtattermusch/grpc,vjpai/grpc,vjpai/grpc,ejona86/grpc,vjpai/grpc,nicolasnoble/grpc,vjpai/grpc,ctiller/grpc