* config/tc-mips.c (append_insn): Use fix_new rather than fix_new_exp
to build the second and third fixups for a composite relocation.
(macro_read_relocs): New function.
(macro_build): Use it.
(s_cpsetup): Pass all three composite relocation codes to macro_build.
Simplify fragging code accordingly.
(s_gpdword): Use fix_new rather than fix_new_exp for the second part
of the composite relocation. Set fx_tcbit in both fixups.