My C++03 project needs an upgrade to C++11, and I can guarantee that at least experimental support for it will be available in all the GCCs I want to use.
However, that may be -std=c++0x or it may be actual -std=c++11 from newer GCC.
How can I form a GNU Makefile that adds the appropriate flag to CXXFLAGS depending on which one will succeed? Bonus points for -std=c++14 support…
I suppose ideally I'd just say "okay, my earliest GCC in use still doesn't have production-ready C++11 support so I should stick with C++03", but meh.