Use correct names for __ibm128 if long double is IEEE 128-bit.

Use correct names for __ibm128 if long double is IEEE 128-bit.

If you are on a PowerPC system where the default long double is IEEE
128-bit (either through the compiler option -mabi=ieeelongdouble or via
the configure option --with-long-double-format=ieee), GCC used the wrong
names for some of the conversion functions for the __ibm128 type.

Internally, GCC uses IFmode for __ibm128 if long double is IEEE 128-bit,
instead of TFmode when long double is IBM 128-bit.  This patch adds the
missing conversions to prevent the 'if' name from being used.

In particular, before the patch, the conversions used were:

    IFmode to DImode signed:	__fixifdi	instead of __fixtfdi
    IFmode to DImode unsigned	__fixunsifti	instead of __fixunstfti
    DImode to IFmode signed:	__floatdiif	instead of __floatditf
    DImode to IFmode unsigned:	__floatundiif	instead of __floatunditf

2022-02-14  Michael Meissner  <meissner@the-meissners.org>

gcc/
	PR target/104253
	* config/rs6000/rs6000.cc (init_float128_ibm): Update the
	conversion functions used to convert IFmode types.

gcc/testsuite/
	PR target/104253
	* gcc.target/powerpc/pr104253.c: New test.