patch 9.1.0616: filetype: Make syntax highlighting off for MS Makefiles

Problem:  filetype: Make syntax highlighting off for MS Makefiles
Solution: Try to detect MS Makefiles and adjust syntax rules to it.
          (Ken Takata)

Highlighting of variable expansion in Microsoft Makefile can be broken.
E.g.:
https://github.com/vim/vim/blob/2979cfc2627d76a9c09cad46a1647dcd4aa73f5f/src/Make_mvc.mak#L1331

Don't use backslash as escape characters if `make_microsoft` is set.
Also fix that `make_no_comments` was not considered if `make_microsoft`
was set.

Also add description for `make_microsoft` and `make_no_comments` to the
documentation and include a very simple filetype test

closes: #15341

Signed-off-by: Christian Brabandt <cb@256bit.org>
Signed-off-by: Ken Takata <kentkt@csc.jp>
diff --git a/src/testdir/test_filetype.vim b/src/testdir/test_filetype.vim
index cee7c21..f8b3ea8 100644
--- a/src/testdir/test_filetype.vim
+++ b/src/testdir/test_filetype.vim
@@ -2646,4 +2646,21 @@
   filetype off
 endfunc
 
+func Test_make_file()
+  filetype on
+
+  " Microsoft Makefile
+  call writefile(['# Makefile for Windows', '!if "$(VIMDLL)" == "yes"'], 'XMakefile.mak', 'D')
+  split XMakefile.mak
+  call assert_equal(1, get(b:, 'make_microsoft', 0))
+  bwipe!
+
+  call writefile(['# get the list of tests', 'include testdir/Make_all.mak'], 'XMakefile.mak', 'D')
+  split XMakefile.mak
+  call assert_equal(0, get(b:, 'make_microsoft', 0))
+  bwipe!
+
+  filetype off
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index f434a13..9ee1592 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    616,
+/**/
     615,
 /**/
     614,