I don't understand the difference. Is "zig cc" more smart to find included files than the other compilers?
zig cc is really, really cool, and it's incredibly generous that it provides zig's benefits to users of C and C++ as well.
With GCC and Clang, I only pay for cross compilation if I need it, so for a fair comparison, the cross-compiler libraries should be installed for GCC and Clang. Also with GCC and Clang, I don't have to worry about a third party (the Zig team) incorporating bug and security fixes from upstream. And with GCC I get support for more platforms.
If I have chosen to use cross-compilation, building for alternative architectures is just as easy as for Zig.