There are two CWG issues related to this:
It looks like the current text addresses this. From 1655 "Is it intended that, for example, a CRLF in the source of a raw string literal is to be represented as a newline character or as the original characters?"
From the current draft:
http://eel.is/c++draft/lex.string#4[Note 2: A source-file new-line in a raw string literal results in a new-line in the resulting execution string literal
. Assuming no whitespace at the beginning of lines in the following example, the assert will succeed:const char* p = R"(a\
b
c)";
assert(std::strcmp(p, "a\\\nb\nc") == 0);
— end note]