This is the next step in dealing with #26. Update seec-cc to behave more like
the clang driver. Essentially it is the clang driver now, with the following
differences:
* it uses SeeC-specific FrontendActions for code generation.
* it never emits native object files (it emits LLVM bitcode instead if -emit-obj is requested).
* it replace linker commands with calls to seec-ld.
* it adds the command line arguments that are required when compiling programs to be used with seec (-fno-builtin, -D_FORTIFY_SOURCE=0, -D__NO_CTYPE=1, -lseecRuntimeTracer, etc.)

We also updated seec-ld to have a better system for passing in arguments that
shouldn't be forwarded to the real linker, but are used by seec-ld itself.