libc: types: add a comment to the "wrong definition" code

Add an explanation comment, so no one in the future
will try to change that part of the code.
Add parasoft tags to suppress a violation in static analysis tool

Signed-off-by: Maksim Masalski <maksim.masalski@intel.com>

lib/libc/minimal/include/sys/types.h

@@ -16,6 +16,10 @@ typedef unsigned int mode_t;
 #if !defined(__ssize_t_defined)
 #define __ssize_t_defined
 
+/* parasoft suppress item MISRAC2012-RULE_20_4-a item MISRAC2012-RULE_20_4-b
+ * "Trick compiler to make sure the type of ssize_t won't be
+ * unsigned long. View details in commit b889120"
+ */
 #define unsigned signed
 typedef __SIZE_TYPE__ ssize_t;
 #undef unsigned