[build, doc, v3] Support Sun symbol versioning in libstdc++-v3, rev. 2

[Paolo Bonzini]

>        config:
>        * gc++filt.m4: New file.

This is ok.

>        contrib:
>        * make_sunver.pl: New file.

Not sure this belongs in contrib.  Probably the toplevel or, for now,
libstdc++-v3, is a better place.

>        libstdc++v3:
>        * acinclude.m4 (GLIBCXX_ENABLE_SYMVERS): Handle sun style.
>        Require GCC_PROG_GNU_CXXFILT.
>        (_GLIBCXX_HAVE_SYMVER_SYMBOL_RENAMING_RUNTIME_SUPPORT): Define
>        unless targetting solaris2*.
>        Include ../config/gc++filt.m4.
>        * configure.host (i?86-*-solaris2*): Set abi_baseline_pair.
>        (sparc-*-solaris2*): Likewise.
>        * src/Makefile.am [ENABLE_SYMVERS_SUN] (version_dep, version_arg):
>        New variables.
>        (libstdc++-symbols.ver-sun): New target.
>        * configure: Regenerate.
>        * config.h.in: Regenerate.
>        * Makefile.in: Likewise.
>        * doc/Makefile.in: Likewise.
>        * include/Makefile.in: Likewise.
>        * libsupc++/Makefile.in: Likewise.
>        * po/Makefile.in: Likewise.
>        * python/Makefile.in: Likewise.
>        * src/Makefile.in: Likewise.
>        * src/atomic.cc: Only define/use _GLIBCXX_ASM_SYMVER if
>        _GLIBCXX_HAVE_SYMVER_RENAMING_RUNTIME_SUPPORT.
>        * src/compatibility.cc: Likewise.
>        * testsuite/Makefile.am (baseline_subdir): Define.
>        (baseline_symbols): Use it.
>        (new-abi-baseline): Likewise.
>        * testsuite/Makefile.in: Regenerate.
>
>        * config/abi/pre/gnu.ver (GLIBCXX_3.4.5): Enclose duplicates in
>        #ifdef HAVE_SYMVER_RENAMING_RUNTIME_SUPPORT.
>        (GLIBCXX_3.4.6): Likewise.
>
>        * doc/xml/manual/configure.xml (--enable-symvers): Document sun
>        style.
>        * doc/html/manual/configure.html: Regenerate.
>
>        * doc/xml/manual/abi.xml: Fix grammar.
>        (Symbol versioning on the libstdc++.so binary): Fix mapfile path.
>        (Incremental bumping of a library pre-defined macro): Fix
>        c++config path.
>        (Incremental bumping of a library pre-defined macro,
>        _GLIBCPP_VERSION): Likewise.
>        (Matching each specific C++ compiler release to a specific set of
>        C++ include files): Fix acinclude.m4 path.
>        (Prerequisites): Allow for Sun linker on Solaris 2.5+.
>        Use proper link to Configuring.
>        Fix acinclude.m4 path.
>        (Checking Active): Allow for additional symbol versioning styles.
>        Provide Solaris 2 example with pvs -r.
>        (Bibliography): Update Linker and Libraries Guide, C++ Migration
>        Guide entries.
>        * doc/html/manual/abi.html: Regenerate

Deferring this to libstdc++ maintainers.

Paolo