ImportC: Support Stringizing operator in C macros

[LightBender]

This C macro:
#define ZSTD_QUOTE(str) #str

Produces no output.

Expected output would be something like:

auto ZSTD_QUOTE(alias sym)()
{
    return sym.stringof;
}

[jmdavis]

The more precise definition of what # is supposed to do can be found here: https://port70.net/~nsz/c/c11/n1570.html#6.10.3.2p2

Making it work in the general case would probably require some sort of string mixin instead, since it could involve expressions whereas alias parameters need symbols, but when the argument is a single symbol, an alias parameter in conjunction with stringof would be close. It still wouldn't quite get there even with single symbols, because ZSTD_QUOTE(foo) would have to become ZSTD_QUOTE!foo, but it would be usable in a similar fashion.