[Bug c/88382] undocumented GNU C extension: C++ raw string literals permitted in GNU C

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88382

--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
The extension is intentionally supported.  Thus, it should be documented.