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/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index f843082..2f8d950 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -1,4 +1,4 @@
-*syntax.txt*	For Vim version 9.1.  Last change: 2024 Jul 23
+*syntax.txt*	For Vim version 9.1.  Last change: 2024 Jul 25
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -2278,7 +2278,7 @@
 displayed line.  If you have a slow machine, and generally deal with emails
 with short headers, you can change this to a smaller value: >
 
-    :let mail_minlines = 30
+	:let mail_minlines = 30
 
 
 MAKE						*make.vim* *ft-make-syntax*
@@ -2289,6 +2289,16 @@
 
 	:let make_no_commands = 1
 
+Comments are also highlighted by default.  You can turn this off by using: >
+
+	:let make_no_comments = 1
+
+Microsoft Makefile handles variable expansion and comments differently
+(backslashes are not used for escape).  If you see any wrong highlights
+because of this, you can try this: >
+
+	:let make_microsoft = 1
+
 
 MAPLE						*maple.vim* *ft-maple-syntax*