libstdc++: Update some baseline_symbols.txt

As we have only one P1 left right now, I think it is the right time
to update abi list files in libstdc++.

Here is an update for x86_64/i?86/s390x/ppc64 linux (aarch64 seems
to be correct already).  For ppc64le it is missing the IEEE128 symver
symbols, but those need further work on the abi checking side.

2021-04-17  Jakub Jelinek  <jakub@redhat.com>

	* config/abi/post/x86_64-linux-gnu/baseline_symbols.txt: Update.
	* config/abi/post/x86_64-linux-gnu/32/baseline_symbols.txt: Update.
	* config/abi/post/i386-linux-gnu/baseline_symbols.txt: Update.
	* config/abi/post/i486-linux-gnu/baseline_symbols.txt: Update.
	* config/abi/post/s390x-linux-gnu/baseline_symbols.txt: Update.
	* config/abi/post/powerpc64-linux-gnu/baseline_symbols.txt: Update.