libstdc++: Update ppc64le baseline_symbols.txt

libstdc++: Update ppc64le baseline_symbols.txt

> Tested on powerpc64{,le}-linux now (-m32/-m64 on be) and while the first
> patch works fine, the second one unfortunately doesn't on either be or le,
> so more work is needed there.

Here are the needed changes to make it work.
For symbols with _LDBL_ substring in version name we already have code to
ignore those if no such symbols appear (but it is slightly incorrect, see
below).
So, this patch does the same thing for symbol versions with _IEEE128_
substring.
The previously incorrectly handled case is that in addition to
FUNC:_ZNKSt17__gnu_cxx_ieee1287num_getIcSt19istreambuf_iteratorIcSt11char_traitsIcEEE14_M_extract_intImEES4_S4_S4_RSt8ios_baseRSt12_Ios_IostateRT_@@GLIBCXX_IEEE128_3.4.29
or
OBJECT:12:_ZTSu9__ieee128@@CXXABI_IEEE128_1.3.13
cases we also have the
OBJECT:0:CXXABI_IEEE128_1.3.13
OBJECT:0:GLIBCXX_IEEE128_3.4.29
cases, which have empty version_name and the name is in that case the
symbol version.  Those need to be ignored too.

2021-04-20  Jakub Jelinek  <jakub@redhat.com>

	* testsuite/util/testsuite_abi.cc (compare_symbols): If any symbol
	versions with _IEEE128_ substring are found, set ieee_version_found
	to true.  Ignore missing symbols with _IEEE128_ in version name if
	!ieee_version_found.  Use i->first as version_name instead of
	i->second.version_name if the latter is empty.
	* config/abi/post/powerpc64-linux-gnu/baseline_symbols.txt: Update.