mpfr: Fix a test case

Normally we don't fix test, but see the comment added into the XML file
for the rationale.

Update the number of tests by the way.

chapter08/mpfr.xml

@@ -41,6 +41,20 @@
   <sect2 role="installation">
     <title>Installation of MPFR</title>
 
+    <!-- https://sympa.inria.fr/sympa/arc/mpfr/2023-01/msg00002.html
+         https://gitlab.inria.fr/mpfr/mpfr/-/commit/5172494c
+
+         Note that it's a different issue from Glibc #30068 we've fixed in
+         chapter08/glibc.xml with a sed.  Normally we just document the
+         test failure, but in this case the particular subtest also serves
+         as an additional guard against Glibc #30068.  So we apply the
+         upstream fix here.   -->
+    <para>Fix a test case based on a bug of old Glibc releases:</para>
+
+<screen><userinput remap="pre">sed -e 's/+01,234,567/+1,234,567 /' \
+    -e 's/13.10Pd/13Pd/'            \
+    -i tests/tsprintf.c</userinput></screen>
+
     <para>Prepare MPFR for compilation:</para>
 
 <screen><userinput remap="configure">./configure --prefix=/usr        \
@@ -58,7 +72,7 @@ make html</userinput></screen>
       Do not skip it under any circumstances.</para>
     </important>
 
-    <para>Test the results and ensure that all 183 tests passed:</para>
+    <para>Test the results and ensure that all 197 tests passed:</para>
 
 <screen><userinput remap="test">make check</userinput></screen>