This patch replaces the following two patches:

This patch replaces the following two patches:

September 24th, 2020:
Message-ID: <20200924203545.GD31597@ibm-toto.the-meissners.org>

October 22nd, 2020:
Message-ID: <20201022220603.GA11658@ibm-toto.the-meissners.org>

This patch rewrites those patches.  In order to run with older GLIBC's, this
patch uses weak references to the IEEE 128-bit conversions to/from string that
are found in GLIBC 2.32.

If the user uses GLIBC 2.32 or later, the Decimal <-> Float128 conversions will
call the functions in that library.  This isn't ideal, as IEEE 128-bit has more
exponent range than IBM 128-bit.

If an older library is used, these patches will convert IEEE 128-bit to IBM
128-bit and do the conversion with IBM 128-bit.  I have tested this with a
compiler configured to use an older library, and it worked for the conversion
if the number could be represented in the IBM 128-bit format.

While most of the Decimal <-> Long double tests now pass when long doubles are
IEEE 128-bit, there are two tests that fails:

    *	c-c++-common/dfp/convert-bfp-6.c
    *	c-c++-common/dfp/convert-bfp-11.c

I have patches for the bfp-11 test (which requires that long double be IBM
128-bit).  I have not looked at the bfp-6 test but I will shortly.

I have tested this patch by doing builds, bootstraps, and make check with 3
builds on a power9 little endian server:

    *   Build one used the default long double being IBM 128-bit;
    *   Build two set the long double default to IEEE 128-bit; (and)
    *   Build three set the long double default to 64-bit.

The compilers built fine providing I recompiled gmp, mpc, and mpfr with the
appropriate long double options.  There were a few differences in the test
suite runs that will be addressed in later patches, but over all it works
well.  This patch is required to be able to build a toolchain where the default
long double is IEEE 128-bit.  Can I check this patch into the master branch for
GCC 11?

libgcc/
2021-01-21  Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/_dd_to_kf.c: New file.
	* config/rs6000/_kf_to_dd.c: New file.
	* config/rs6000/_kf_to_sd.c: New file.
	* config/rs6000/_kf_to_td.c: New file.
	* config/rs6000/_sd_to_kf.c: New file.
	* config/rs6000/_sprintfkf.c: New file.
	* config/rs6000/_sprintfkf.h: New file.
	* config/rs6000/_strtokf.h: New file.
	* config/rs6000/_strtokf.c: New file.
	* config/rs6000/_td_to_kf.c: New file.
	* config/rs6000/quad-float128.h: Add new declarations.
	* config/rs6000/t-float128 (fp128_dec_funcs): New macro.
	(fp128_decstr_funcs): New macro.
	(ibm128_dec_funcs): New macro.
	(fp128_ppc_funcs): Add the new conversions.
	(fp128_dec_objs): Force Decimal <-> __float128 conversions to be
	compiled with -mabi=ieeelongdouble.
	(fp128_decstr_objs): Force __float128 <-> string conversions to be
	compiled with -mabi=ibmlongdouble.
	(ibm128_dec_objs): Force Decimal <-> __float128 conversions to be
	compiled with -mabi=ieeelongdouble.
	(FP128_CFLAGS_DECIMAL): New macro.
	(IBM128_CFLAGS_DECIMAL): New macro.
	* dfp-bit.c (DFP_TO_BFP): Add PowerPC _Float128 support.
	(BFP_TO_DFP): Add PowerPC _Float128 support.
	* dfp-bit.h (BFP_KIND): Add new binary floating point kind for
	IEEE 128-bit floating point.
	(DFP_TO_BFP): Add PowerPC _Float128 support.
	(BFP_TO_DFP): Add PowerPC _Float128 support.
	(BFP_SPRINTF): New macro.