Add docs for -MD and -MMD

Index: doc/ccomp.1
--- doc/ccomp.1.orig
+++ doc/ccomp.1
@@ -110,7 +110,7 @@ Pass comma separated arguments in <args> to the prepro
 Pass argument <arg> to the preprocessor.
 .
 .TP
-.BR \-C ", " \-CC ", " \-finput-charset ", " \-idirafter ", " \-imacros ", " \-iquote ", " \-isystem ", " \-M ", " \-MF ", " \-MG ", " \-MM ", " \-MP ", " \-MQ ", " \-MT  ", " \-nostdinc ", " \-P
+.BR \-C ", " \-CC ", " \-finput-charset ", " \-idirafter ", " \-imacros ", " \-iquote ", " \-isystem ", " \-M ", " \-MD ", " \-MF ", " \-MG ", " \-MM ", " \-MMD" , " \-MP ", " \-MQ ", " \-MT  ", " \-nostdinc ", " \-P
 For GNU backends these options are recognized by CompCert and passed through to the preprocessor.
 .
 .SS
