Constant C string fix

The constant C string implementation in CodeGenModule is incorrect. When you do str + "\0", you are appending a C string to the string, and so it inserts all of the characters before the first NULL byte into the C++ string. Since \0 is the first byte, (str + "\0") == str. This means anything calling GetAddrOfConstantCString() is getting the wrong result. I found this due to the ObjC class lookup function being passed unterminated strings - it also explains the random crashes on Linux in the ObjC load function. I haven't checked if this pattern is being used anywhere else.

Index: CodeGenModule.cpp

Wow, scary. Fixed here, thanks!
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20081208/010036.html

-Chirs

Not that it really matters, but it looks like the code for __func__
and friends was using the same pattern.

-Eli