* nix/boost: This directory and all files inside it are removed.
* nix/libstore/build.cc (Goal::trace): Use ‘std::string’ instead of ‘const format &’.
(DerivationGoal::startBuilder, ...): Use ‘std::format’ or ‘std::vformat’ instead of ‘boost::format’.
* nix/libstore/builtins.cc (builtinDownload): Same.
* nix/libstore/derivations.cc (DerivationOutput::parseHashInfo, ...): Same.
* nix/libstore/gc.cc (LocalStore::openGCLock, ...): Same.
* nix/libstore/globals.cc (Settings::_get): Same.
* nix/libstore/local-store.cc: (checkStoreNotSymlink, ...): Same.
* nix/libstore/misc.cc (dfsVisit, showBytes): Same
* nix/libstore/optimise-store.cc (makeWritable, ...): Same.
* nix/libstore/pathlocks.cc (openLockFile, ...): Same.
* nix/libstore/references.cc (search, scanForReferences): Same.
* nix/libstore/sqlite.hh (throwSQLiteError): Use ‘std::string’ instead of ‘const format &’.
* nix/libstore/sqlite.cc (throwSQLiteError): Use ‘std::string’ instead of ‘const format &’.
* nix/libstore/store-api.cc (assertStorePath, ...): Use ‘std::format’ instead of ‘boost::format’.
* nix/libutil/affinity.cc (setAffinityTo): Same.
* nix/libutil/archive.cc (dumpContents, ...): Same.
* nix/libutil/hash.cc (parseHash, parseHash32, parseHash16or32, hashFile): Same.
* nix/libutil/hash.hh (parseHash, parseHash32, parseHash16or32, isHash): Same.
* nix/libutil/serialise.cc : Add ‘<cassert>’ header file.
* nix/libutil/spawn.cc (addPhaseAfter, ...): Use ‘std::format’ instead of ‘boost::format’.
* nix/libutil/types.hh (FormatOrString): Removed.
(BaseError, BaseError::addPrefix, SysError, MakeError):
Use ‘std::string or std::string_view’ instead of ‘FormatOrString’.
* nix/libutil/util.hh (Nest::open, printMsg_, warnOnce, expect): Same.
* nix/libutil/util.cc (BaseError::BaseError, ...): Same.
(writeToStderr, _interrupted): Use std::uncaught_exceptions() instead of std::uncaught_exception()
* nix/nix-daemon/nix-daemon.cc (performOp, ...): Same.
* nix/nix-daemon/guix-daemon.cc (string_to_bool, ...): Same.
* nix/local.mk: Remove ‘libformat.a’ from ‘noinst_LIBRARIES’,
remove ‘libformat_a_SOURCES’ and ‘libformat_headers’,
remove ‘libformat_a_CPPFLAGS’ from ‘libutil_a_CPPFLAGS’ and ‘guix_daemon_LDADD’,
update ‘AM_CXXFLAGS’ to ‘-std=c++20’.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

Remove .gitignore entries where they match source files that are tracked in
Git.  This is relevant to me at least, as some code searching tools use
.gitignore files and will ignore matched files.

* nix/boost/format/exceptions.hpp (too_few_args): Fix typo.
  (too_many_args): Fix typo.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

* configure.ac: Call `AC_USE_SYSTEM_EXTENSIONS', and
  `GUIX_SYSTEM_TYPE'.  Add `--with-store-dir' option, and substitute
  `storedir'.  Include `config-daemon.ac'.
* config-daemon.ac: New file.
* Makefile.am [BUILD_DAEMON]: Include `daemon.am'.
* daemon.am: New file.
* m4/guix.m4 (GUIX_SYSTEM_TYPE): New macro.

* nix/libutil/gcrypt-hash.cc, nix/libutil/gcrypt-hash.hh,
  nix/libutil/md5.h, nix/libutil/sha1.h, nix/libutil/sha256.h,
  nix/nix-daemon/guix-daemon.cc, nix/nix-daemon/shared.hh: New files.