https://gcc.gnu.org/gcc-4.5/changes.html

Looks like it is on purpose:
C++0x raw strings are supported for C++ and for C with -std=gnu99.



https://inbox.sourceware.org/gcc-patches/20080912132007.GA9666@hs20-bc2-1.build.redhat.com/

Thanks!

-std=gnu89 is meant for really old programs, and the raw string literal support changes behavior, so it isn't a pure extension on what wasn't valid before, e.g. consider
#define R
#define b
const char * square(void) {
    return R"(a"b"a)";
}
in -std=c89 or -std=gnu89 this is return "(aa)"; while in -std=gnu99 return "a\"b\"a";

Yeah, we figured that that was why they’re not supported in `-gnu89` mode, but I thought I’d ask just to be sure.

Then this isn't a valid bug report.

Oops, the mouse scroll wheel is too sensitive and I selected the wrong resolution :(.