Implement PR614:

These changes modify the makefiles so that the output of flex and bison are
placed in the SRC directory, not the OBJ directory. It is intended that they
be checked in as any other LLVM source so that platforms without convenient
access to flex/bison can be compiled. From now on, if you change a .y or
.l file you *must* also commit the generated .cpp and .h files.

llvm-svn: 23115