Coverity, maker of c++ static analysis software, and where I used to work, has published a paper about their experience trying to parse customer code. It turns out that 'The language people code in? The strings their compiler accepts'

So yes, it is quite common to use syntax not available in other compilers. Most code is vetted against only one compiler to begin with.

http://www.stanford.edu/~engler/BLOC-coverity.pdf