and why the book says \--enable-shared
The "--enable-shared" option takes care, that
libbfd-2.17.so is created ( "so" means shared object.)
Your errors : I don't know ... libbfd-2.17.so
should be present in your "build-binutils"
P.S.: 1) No reason to use the backslash, it can all
be made up to a "one line configure".
2) If the backslash is used, a <space> must be present
after the backslash, like this : '\ --enable-shared' .
3) The backslash is used only to break a line.