Option to disable -nodefaultlibs to the linker

[alexcrichton]

Currently the compiler unconditionally passes -nodefaultlibs (or the platform equivalent) to the linker. Unfortunately though this actually causes linking to fail in some circumstances. Some investigation has shown that when compiled with -fsanitize=address this has been seen to cause problems and cause link errors.

While there may be more bugs to fix here on various sides, we should have an option to disable passing this flag!

[Earlz]

I literally just ran into this as well, though I assumed it was due to me using no_std.