The -Wpointer-sign warning text is inappropriate for describing the incompatible pointer conversion between plain char and explicitly signed/unsigned char (whichever plain char has the same range as) and vice versa.
Specifically, in part, it reads "converts between pointers to integer types with different sign". This patch changes that portion to read instead as "converts between pointers to integer types where one is of the unique plain char type and the other is not" when one of the types is plain char.
C17 subclause 220.127.116.11 indicates that the conversions resulting in -Wpointer-sign warnings in assignment-like contexts are constraint violations. This means that strict conformance requires a diagnostic for the case where the message text is wrong before this patch. The lack of an even more specialized warning group is consistent with GCC.