This happens to work on Linux where the two major compilers (gcc and clang) are (mostly?) compatible. Windows is a different story: C++ code build with MSCV is generally not compatible with GCC/clang and vice versa, the most notable differences being vtable layout and default 32-bit calling conventions.
But "C++ on Linux" isn't "C++". It's a subset of C++ usage. The lack of competing compilers on some OS might be a feature of those OS, or in the eyes of some mabye even a failure of those OS, but it's certainly no feature of the language. ABI compatibility isn't about using the same binary on different OS, it's about running binaries from different compilers/compiler versions/compiler configurations in the same process.
