Yup, as someone who's done x-platform C++(Windows/OSX/X360/PS3/etc) for a large part of my career the cross platform support is incredibly well done.
Not having to deal with differences between MSVC, LLVM, GCC and other obscure toolchains is a blessing.
This is one reason why I enjoyed using Java so much in the early days, even without JIT.
The differences between MSVC, LLVM, GCC are nothing to worry about, compared with the early days of C89 or C++ARM in the process of being standardized, coupled with different levels of POSIX support.
I actually do think that Rust's type system helps a bit, because it forces me to consider weird portability issues (such as the way Windows permits slightly invalid Unicode, which Rust represents as OSString instead of String).
And of course, cross-compilation with MinGW is a real help. Sadly, OpenSSL still poses a fair number of portability issues, since it's notoriously difficult to link statically.