patch 9.1.1321: filetype: MS ixx and mpp files are not recognized

Problem:  filetype: MS ixx and mpp files are not recognized
Solution: detect *.mpp and *.ixx files as c++ filetype
          (Hampus Avekvist)

closes: #17155

Signed-off-by: Hampus Avekvist <hampus.avekvist@hey.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_filetype.vim b/src/testdir/test_filetype.vim
index 91460ce..6ec55ae 100644
--- a/src/testdir/test_filetype.vim
+++ b/src/testdir/test_filetype.vim
@@ -188,7 +188,7 @@
     cook: ['file.cook'],
     corn: ['file.corn'],
     cpon: ['file.cpon'],
-    cpp: ['file.cxx', 'file.c++', 'file.hh', 'file.hxx', 'file.hpp', 'file.ipp', 'file.moc', 'file.tcc', 'file.inl', 'file.tlh', 'file.cppm', 'file.ccm', 'file.cxxm', 'file.c++m'],
+    cpp: ['file.cxx', 'file.c++', 'file.hh', 'file.hxx', 'file.hpp', 'file.ipp', 'file.ixx', 'file.moc', 'file.tcc', 'file.inl', 'file.tlh', 'file.cppm', 'file.ccm', 'file.cxxm', 'file.c++m', 'file.mpp'],
     cqlang: ['file.cql'],
     crm: ['file.crm'],
     crontab: ['crontab', 'crontab.file', '/etc/cron.d/file', 'any/etc/cron.d/file'],
diff --git a/src/version.c b/src/version.c
index c255361..4c9f4ce 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1321,
+/**/
     1320,
 /**/
     1319,