Remove redundant -Wpointer-sign CFLAG

-Wpointer-sign is implied with -Wall, which we use when building with
--enable-gcc-warnings.

configure.in

@@ -99,7 +99,7 @@ AC_ARG_ENABLE(gcc-hardening,
 [if test x$enableval = xyes; then
     CFLAGS="$CFLAGS -D_FORTIFY_SOURCE=2 -fstack-protector-all"
     CFLAGS="$CFLAGS -fwrapv -fPIE -Wstack-protector"
-    CFLAGS="$CFLAGS -Wpointer-sign --param ssp-buffer-size=1"
+    CFLAGS="$CFLAGS --param ssp-buffer-size=1"
     LDFLAGS="$LDFLAGS -pie"
 fi])