Don't set INCDIRS in create_target_vars:

* This eliminates the need for INCDIRS to be simply expanded
Use prepend_gcc_incdirs in recipes and not variable assignment:

* The recipe which knows the include directory option because it knows
  what command is used to generate teh object file.
Use prepend_gcc_libdirs in the target rule:

* This puts the command specific option generation where it should be.
* Also remove -rpath-link generation.