fetch G_CPP20_SOURCES.

updates for GCC 12 (relatively tiny).

- gcov-iov.h is now called version.h and we build it directly.
- need to explicitly ask for bversion.h gtyp-input.list to be built.

don't rename codecvt.cc here, do it in a Makefile when consumed.

since the Makefiles already need updates for these, it's easier
if all of the changes are there.

fetch experimental_headers, experimental_bits_headers, and ext_host_headers
to install install experimental/* and ext/opt_random.h.

fetch omp-device-properties.h and don't try to fetch sanitizer
stuff automatically yet.

make mknative-gcc.old for GCC 9. begin to update mknative-gcc for GCC 10.

more consolidation and properly condition all variables like previously.

consolidate a bunch of libstdc++ variable collection.

oops, pull out the value of pstl_headers.

pass down earm* not earmv5* to mknative-gcc.

disable fetching stuff from libsanitizer for now. it needs libstdc++
to build in mknative using gcc makefiles, and our locale changes break
the "normal" build of this.

make sure MKNATIVE_TARGET is

disable fetching stuff from libsanitizer for now. it needs libstdc++
to build in mknative using gcc makefiles, and our locale changes break
the "normal" build of this.

make sure MKNATIVE_TARGET is always set. since mknative-gcc doesn't
care about the version any more (we keep two versions for gcc/gcc.old)
simply set it to "gcc".

show more ...

pull out a few more things for GCC 9.

port to GCC 9.3.

set _OUTDIRBASE depending on $0, and then set _OUTDIR based on this.
now you can copy mknative-gcc to mknative-gcc.old without edit.

mknative-gcc is for GCC 8.4.
mknative-gcc.old is supposed to be for GCC 7, but is the GCC 6
version. update it and mark it for GCC 7.5.

arm needs more files

copy arm-cpu.h and arm-isa.h for arm platforms.

pull out libstdc++ config.h as-is, for gnu.ver processing.
pull out the cxx11_sources and cxx98_sources values to avoid hard coding.

- build the gthr*.h files to be installed on the fly, instead of
having dozens of copies of the same thing in the tree.
- don't fetch any gthr*.h files.
- delete ancient gthr-tpf.h that was removed

- build the gthr*.h files to be installed on the fly, instead of
having dozens of copies of the same thing in the tree.
- don't fetch any gthr*.h files.
- delete ancient gthr-tpf.h that was removed in GCC 4.8 or so.

this should fix the call_once tests for real now.

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common-target source list is MD. make it so.

- don't getlinks here, they're no longer used.
- pullout the libcommon, libcommon-target and libgomp source list so they
don't have to be hard coded in the reachover makefile

- use --with-default-libstdcxx-abi=new for GCC, otherwise we get the
old ABI with --disable-libstdcxx-dual-abi
- fix libbacktrace mknative
- find gthr-default.h for libstdc++ mknative
- fetch FILES

- use --with-default-libstdcxx-abi=new for GCC, otherwise we get the
old ABI with --disable-libstdcxx-dual-abi
- fix libbacktrace mknative
- find gthr-default.h for libstdc++ mknative
- fetch FILESYSTEM_SOURCES

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make includes works now.

pull out more data needed for headers and fix gthr-defaults.h.

libgcc_s has multiple symbols.

also pull out these variables:
enable_execute_stack
unwind_header
md_unwind_header
sfp_machine_header
thread_header

also pullout INTERNAL_CFLAGS for the libgcc build, where it may have
-DHAVE_CC_TLS defined on the command line. (we already collect all
the other components.)