libstd++: : Add workaround for as Error: file number less than one error [PR98708]

libstd++: : Add workaround for as Error: file number less than one error [PR98708]

As mentioned in the PR, since the switch to DWARF5 by default instead of
DWARF4, gcc fails to build when configured against recent binutils.

The problem is that cxx11-ios_failure* is built in separate steps,
-S compilation (with -g -O2) followed by some sed and followed by
-c -g -O2 -g0 assembly.  When gcc is configured against recent binutils
and DWARF5 is the default, we emit .file 0 "..." directive on which the
assembler then fails (unless --gdwarf-5 is passed to it, but we don't want
that generally because on the other side older assemblers don't like -g*
passed to it when invoked on *.s file with compiler generated debug info.

I hope the bug will be fixed soon on the binutils side, but it would be nice
to have a workaround.

The following patch is one of the possibilities, another one is to do that
but add configure check for whether it is needed,
essentially
echo 'int main () { return 0; }' > conftest.c
${CXX} ${CXXFLAGS} -g -O2 -S conftest.c -o conftest.s
${CXX} ${CXXFLAGS} -g -O2 -g0 -c conftest.s -o conftest.o
and if the last command fails, we need that -gno-as-loc-support.
Or yet another option would be I think do a different check, whether
${CXX} ${CXXFLAGS} -g -O2 -S conftest.c -o conftest.s
${CXX} ${CXXFLAGS} -g -O2 -c conftest.s -o conftest.o
works and if yes, don't add the -g0 to cxx11-ios_failure*.s assembly.

2021-01-18  Jakub Jelinek  <jakub@redhat.com>

	PR debug/98708
	* src/c++11/Makefile.am (cxx11-ios_failure-lt.s, cxx11-ios_failure.s):
	Compile with -gno-as-loc-support.
	* src/c++11/Makefile.in: Regenerated.