fp-bit.h: Define macros for TFmode floating-point constants in IEEE quad TFmode type.

* config/fp-bit.h: Define macros for TFmode floating-point
constants in IEEE quad TFmode type.  Declare functions according
to L_ macros.
(TMODES): Define if __LDBL_MANT_DIG__ is 113.
(TFtype, TItype, UTItype): Define if TMODES is defined.
(MAX_UDI_INT, MAX_DI_INT, BITS_PER_DI): Likewise.
(F_T_BITOFF, D_T_BITOFF): Define.
(IMPLICIT_1, IMPLICIT_2): Cast constants to types that are
guaranteed to be wide enough.
* config/fp-bit.c: Check for L_ macros for tf functions.
(__thenan_tf): New.
(nan): Adjust.
(pack_d, unpack_d): Support IEEE 854 quad type.
(_fpmul_parts): Support TFmode.  Compute exponent adjustment
from FRAC_NBITS, FRAC_BITS and NGARDS.
(usi_to_float): Cast constants to be shifted to fractype
instead of assuming long long is wide enough.
(sf_to_tf, df_to_tf, __make_tp, tf_to_df, tf_to_sf): New.

From-SVN: r61835