Hi

     Here is the patch to remove the useless _Is_pod_comparator 
_Rb_tree_impl template parameter. As this is an ABI breaking change it 
is limited to the versioned namespace mode and the patch also bump the 
namespace version.

     Working on this patch I wonder if the gnu-versioned-namespace.ver 
is really up to date. The list of export expressions is far smaller than 
the one in gnu.ver. Would the testsuite show that some symbols are not 
properly exported ?

     Bump version namespace.
     * config/abi/pre/gnu-versioned-namespace.ver: Bump version namespace
     from __7 to __8. Bump GLIBCXX_7.0 into GLIBCXX_8.0.
     * include/bits/c++config: Adapt.
     * include/bits/regex.h: Adapt.
     * include/experimental/bits/fs_fwd.h: Adapt.
     * include/experimental/bits/lfts_config.h: Adapt.
     * include/std/variant: Adapt.
     * python/libstdcxx/v6/printers.py: Adapt.
     * testsuite/libstdc++-prettyprinters/48362.cc: Adapt.
     * include/bits/stl_tree.h (_Rb_tree_impl<>): Remove _Is_pod_comparator
     template parameter when version namespace is active.

Tested under Linux x86_64 with version namespace.

Ok to commit ?

François