Add getpayload, getpayloadf, getpayloadl.

Add getpayload, getpayloadf, getpayloadl.

TS 18661-1 defines functions for manipulating the payloads of NaNs.
This patch implements the getpayload functions for glibc; these
extract the NaN payload (from an argument passed as a pointer, for
which corresponding libm-test support is added) and return it in the
same floating-point type.  The return value of these functions is
unspecified for non-NaN arguments; the patch does the simplest thing
to implement, which is that the functions do not check whether the
argument is a NaN and just treat the relevant bits of the
representation as a payload regardless.  A conversion from integer to
floating-point is used to produce the required return value, except in
the ldbl-128 case; as 128-bit integers are not supported for all
configurations using ldbl-128, the code constructs the required
floating-point representation of the return value directly instead.

Tested for x86_64, x86, mips64 and powerpc.

	* math/bits/mathcalls.h [__GLIBC_USE (IEC_60559_BFP_EXT)]
	(getpayload): New declaration.
	* math/Versions (getpayload): New libm symbol at version
	GLIBC_2.25.
	(getpayloadf): Likewise.
	(getpayloadl): Likewise.
	* math/Makefile (libm-calls): Add s_getpayloadF.
	* math/libm-test.inc: Include <nan-high-order-bit.h>.
	(struct test_f_f_data): Add comment.
	(RUN_TEST_fp_f): New macro.
	(RUN_TEST_LOOP_fp_f): Likewise.
	(getpayload_test_data): New array.
	(getpayload_test): New function.
	(main): Call getpayload_test.
	* math/gen-libm-test.pl (parse_args): Handle 'p' in argument
	descriptor.
	* manual/arith.texi (FP Bit Twiddling): Document getpayload,
	getpayloadf and getpayloadl.
	* manual/libm-err-tab.pl: Update comment on interfaces without
	ulps tabulated.
	* sysdeps/ieee754/dbl-64/s_getpayload.c: New file.
	* sysdeps/ieee754/dbl-64/wordsize-64/s_getpayload.c: Likewise.
	* sysdeps/ieee754/flt-32/s_getpayloadf.c: Likewise.
	* sysdeps/ieee754/ldbl-128/s_getpayloadl.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_getpayloadl.c: Likewise.
	* sysdeps/ieee754/ldbl-96/s_getpayloadl.c: Likewise.
	* sysdeps/nacl/libm.abilist: Update.
	* sysdeps/unix/sysv/linux/aarch64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/alpha/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/arm/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/hppa/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/i386/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/ia64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/coldfire/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/m680x0/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/microblaze/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/nios2/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libm-le.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sh/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/tile/tilepro/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/x32/libm.abilist: Likewise.