Def signedness != signed != unsigned for char

When checking for exact compatibility between types (such as in
__builtin_types_compatible_p) consider the case of default signedness to
be incompatible with both of the explicit signedness for char. That is,
char is incompatible with signed char *and* unsigned char, no matter
what the default signedness for char is.

tcc-doc.texi

@@ -970,7 +970,7 @@ be the best solution.
 #define VT_BITFIELD   0x0040  /* bitfield modifier */
 #define VT_CONSTANT   0x0800  /* const modifier */
 #define VT_VOLATILE   0x1000  /* volatile modifier */
-#define VT_SIGNED     0x2000  /* signed type */
+#define VT_DEFSIGN    0x2000  /* signed type */
 
 #define VT_STRUCT_SHIFT 18   /* structure/enum name shift (14 bits left) */
 @end example