Fix various compatibility problems with newer GCC.

This is an amalgamation of these upstream commits:

  https://git.savannah.gnu.org/cgit/src-highlite.git/commit/?id=904949c9026cb772dc93fbe0947a252ef47127f4
  https://git.savannah.gnu.org/cgit/src-highlite.git/commit/?id=ab9fe5cb9b85c5afab94f2a7f4b6d7d473c14ee9

diff --git a/lib/srchilite/fileutil.cc b/lib/srchilite/fileutil.cc
index 59a6d64..963178c 100644
--- a/lib/srchilite/fileutil.cc
+++ b/lib/srchilite/fileutil.cc
@@ -48,7 +48,7 @@ void set_file_util_verbose(bool b) {
 // FIXME avoid using a global variable
 std::string start_path;
 
-string readFile(const string &fileName) throw (IOException) {
+string readFile(const string &fileName) {
     ifstream file(fileName.c_str());
 
     if (!file.is_open()) {
diff --git a/lib/srchilite/fileutil.h b/lib/srchilite/fileutil.h
index 7335a9b..042eb56 100644
--- a/lib/srchilite/fileutil.h
+++ b/lib/srchilite/fileutil.h
@@ -27,7 +27,7 @@ extern std::string start_path;
  * @return the contents of the file
  * @throw IOException
  */
-string readFile(const string &fileName) throw (IOException);
+string readFile(const string &fileName);
 
 //char *read_file(const string &fileName);
 
diff --git a/lib/tests/stdboosterror.h b/lib/tests/stdboosterror.h
index 568545b..d59bfa6 100644
--- a/lib/tests/stdboosterror.h
+++ b/lib/tests/stdboosterror.h
@@ -4,7 +4,7 @@
 #include <boost/regex/pattern_except.hpp>
 
 static boost::regex_error
-        std_boost_exception(boost::regex_error(boost::regex_constants::error_bad_pattern));
+        std_boost_exception = boost::regex_error(boost::regex_constants::error_bad_pattern);
 
 /**
  * returns the string representing a standard exception (which
diff --git a/lib/tests/test_wordtokenizer_main.cpp b/lib/tests/test_wordtokenizer_main.cpp
index 40e23b1..11ba389 100644
--- a/lib/tests/test_wordtokenizer_main.cpp
+++ b/lib/tests/test_wordtokenizer_main.cpp
@@ -11,6 +11,14 @@
 using namespace std;
 using namespace srchilite;
 
+/*
+ * We have to use 'std' namespaces because 'WordTokenizer::WordTokenizerResults::value_type'
+ * is an std::pair<std::string, std::string> in disguise. We have to place 'operator<<()'
+ * into the same namespace for ADL to work. Otherwise gcc-12 or clang-13 can't find the
+ * overload.
+ */
+namespace std {
+
 static ostream &operator <<(ostream &os, const WordTokenizer::WordTokenizerResults::value_type &);
 
 ostream &operator <<(ostream &os, const WordTokenizer::WordTokenizerResults::value_type &token) {
@@ -23,6 +31,8 @@ ostream &operator <<(ostream &os, const WordTokenizer::WordTokenizerResults::val
     return os;
 }
 
+}
+
 int main() {
     WordTokenizer::WordTokenizerResults tokens;
 f.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/htmlxref.cnf: Update from Texinfo.  Add entries for "mes",
"guix.ru", and "guix.zh_CN".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-05-04 23:07:38 +0200'>2019-05-04</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=e8f8363cdebb24dc359cadba7ae0a689fb21fb99'>doc: Update htmlxref.cnf.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/htmlxref.cnf (G): Switch to https.
(geiser, guix.de, guix.es, hurd): New entries.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-07-05 22:16:10 +0200'>2018-07-05</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=c35f77c5a07690fc9d369ed4b751a5a9e5de6cf1'>doc: Update URL of the Emacs-Guix manual.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/htmlxref.cnf (EMACS_GUIX): Update URL.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-07-05 22:13:23 +0200'>2018-07-05</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=56b4dabc2ba3446ff212e0d4d9e2df15fc25e88f'>doc: Mention translations of the manual.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix.texi (Top): Add note about l10n.
* doc/htmlxref.cnf: Add "guix.fr".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-05-30 18:30:39 +0300'>2017-05-30</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=f753c2829913a9bb61dc266f4b1db8275e34a461'>doc: htmlxref: Fix link to Emacs-Guix manual.</a><span class='msg-avail'>...<span class='msg-tooltip'>Reported-by: Ludovic Courtès &lt;ludo@gnu.org&gt;

This fixes a regression introduced by commit
8ca0c88a894c685b624757e38ee7663534f03460.

* doc/htmlxref.cnf (EMACS_GUIX): Fix the link to 'html_node'.
</span></span></td><td>Alex Kost</td></tr>
<tr><td><span title='2017-05-04 22:45:53 +0300'>2017-05-04</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=8ca0c88a894c685b624757e38ee7663534f03460'>doc: Add references to Emacs-Guix manual.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/htmlxref.cnf: Add links to the real manual.
* doc/contributing.texi (Formatting Code): Add reference to it.
* doc/guix.texi (Package Management): Likewise.
</span></span></td><td>Alex Kost</td></tr>