I didn't try getting rid of the c++0x one, I simply added the gnu one. I don't know if that means there is something peculiar to my setup. This was against android 10, fwiw. I think other platforms this may not be a problem, there was more of a write-up about this (I think platform and C vs C++ were mentioned), but for me the flag worked.
If its resizing the icons, should I be using an .svg file instead of .png?
Ok, seems like having both flags is the way to do it, I'll tweak that.
I hadn't added support for using SVG for icons, but it'd be a good format for that, and is easy enough to add, so I'll make sure it supports that too, thanks!