Target FP: Merge doublest.c and dfp.c into target-float.c

Target FP: Merge doublest.c and dfp.c into target-float.c

Now that all target FP operations are performed via target-float.c,
this file remains the sole caller of functions in doublest.c and dfp.c.
Therefore, this patch merges the latter files into the former and
makes all their function static there.

gdb/ChangeLog:
2017-11-06  Ulrich Weigand  <uweigand@de.ibm.com>

	* Makefile.in (SFILES): Remove doublest.c and dfp.c.
	(HFILES_NO_SRCDIR): Remove doublest.h and dfp.h.
	(COMMON_OBS): Remove doublest.o and dfp.o.
	Do not build target-float.c (instead of doublest.c)
	with -Wformat-nonliteral.

	* doublest.c: Remove file.
	* doublest.h: Remove file.
	* dfp.c: Remove file.
	* dfp.h: Remove file.

	* target-float.c: Do not include "doublest.h" and "dfp.h".
	(DOUBLEST): Move here from doublest.h.
	(enum float_kind): Likewise.
	(FLOATFORMAT_CHAR_BIT): Likewise.
	(FLOATFORMAT_LARGEST_BYTES): Likewise.
	(floatformat_totalsize_bytes): Move here from doublest.c.  Make static.
	(floatformat_precision): Likewise.
	(floatformat_normalize_byteorder, get_field, put_field): Likewise.
	(floatformat_is_negative, floatformat_classify, floatformat_mantissa):
	Likewise.
	(host_float_format, host_double_format, host_long_double_format):
	Likewise.
	(floatformat_to_string, floatformat_from_string): Likewise.
	(floatformat_to_doublest): Likewise.  Also, inline the original
	convert_floatformat_to_doublest.
	(floatformat_from_doublest): Likewise.  Also, inline the original
	convert_floatformat_from_doublest.

	Include "dpd/decimal128.h", "dpd/decimal64.h", and "dpd/decimal32.h".
	(MAX_DECIMAL_STRING): Move here from dfp.c.
	(match_endianness): Likewise.
	(set_decnumber_context, decimal_check_errors): Likewise.
	(decimal_from_number, decimal_to_number): Likewise.
	(decimal_to_string, decimal_from_string): Likewise.  Make static.
	(decimal_from_longest, decimal_from_ulongest): Likewise.
	(decimal_to_longest): Likewise.
	(decimal_binop, decimal_is_zero, decimal_compare): Likewise.
	(decimal_convert): Likewise.