* Makefile.in (D32PBIT_FUNCS): New.
(D64PBIT_FUNCS, D128PBIT_FUNCS): Likewise.
(libgcc.mk): Set D32PBIT, D64PBIT, D128PBIT, D32PBIT_FUNCS,
D64PBIT_FUNCS and D128PBIT_FUNCS.
(LIBGCC_DEPS): Include $(D32PBIT), $(D64PBIT), $(D128PBIT).
* mklibgcc.in Bring in the DFP support code if D32PBIT, D64PBIT or
D128PBIT are set.
(decnumber_dep): Define.
* doc/libgcc.texi (Decimal float library routines): New node.
* config/dfp-bit.h, config/dfp-bit.c: New files.