guix: use libtool 2.4.7

As of version 2.4.7, libtool now respects ARFLAGS, which we use, and has
changed the default ARFLAGS from cru to cr (which we also do, see
configure).

This eliminates spammy `ar` output such as:
```bash
  CXXLD    libunivalue.la
/root/.guix-profile/bin/x86_64-linux-gnu-ar: `u' modifier ignored since `D' is the default (see `U')
  AR       libbitcoin_zmq.a
  AR       libbitcoin_consensus.a
  CXXLD    crypto/libbitcoin_crypto_base.la
  CXXLD    crypto/libbitcoin_crypto_sse41.la
/root/.guix-profile/bin/x86_64-linux-gnu-ar: `u' modifier ignored since `D' is the default (see `U')
/root/.guix-profile/bin/x86_64-linux-gnu-ar: `u' modifier ignored since `D' is the default (see `U')
  CXXLD    crypto/libbitcoin_crypto_avx2.la
  CXXLD    crypto/libbitcoin_crypto_x86_shani.la
  CXXLD    leveldb/libleveldb.la
/root/.guix-profile/bin/x86_64-linux-gnu-ar: `u' modifier ignored since `D' is the default (see `U')
  CXXLD    crc32c/libcrc32c.la
/root/.guix-profile/bin/x86_64-linux-gnu-ar: `u' modifier ignored since `D' is the default (see `U')
  CXXLD    leveldb/libmemenv.la
/root/.guix-profile/bin/x86_64-linux-gnu-ar: `u' modifier ignored since `D' is the default (see `U')
/root/.guix-profile/bin/x86_64-linux-gnu-ar: `u' modifier ignored since `D' is the default (see `U')
/root/.guix-profile/bin/x86_64-linux-gnu-ar: `u' modifier ignored since `D' is the default (see `U')
  AR       libbitcoin_cli.a
```

Libtool 2.4.7 release notes:
https://lists.gnu.org/archive/html/autotools-announce/2022-03/msg00000.html

contrib/guix/manifest.scm

@@ -581,7 +581,7 @@ inspecting signatures in Mach-O binaries.")
         xz
         ;; Build tools
         gnu-make
-        libtool
+        libtool-2.4.7
         autoconf-2.71
         automake
         pkg-config