Add -Wobsolete to RGBFIX and RGBGFX, and deprecate rgbfix -O

src/fix/main.cpp

@@ -778,6 +778,7 @@ int main(int argc, char *argv[]) {
 			break;
 
 		case 'O':
+			warning(WARNING_OBSOLETE, "'-O' is deprecated; use '-Wno-overwrite' instead");
 			warnings.processWarningFlag("no-overwrite");
 			break;
 

src/fix/warning.cpp

@@ -12,6 +12,7 @@ Diagnostics<WarningLevel, WarningID> warnings = {
     },
     .warningFlags = {
         {"mbc",        LEVEL_DEFAULT   },
+        {"obsolete",   LEVEL_DEFAULT   },
         {"overwrite",  LEVEL_DEFAULT   },
         {"sgb",        LEVEL_DEFAULT   },
         {"truncation", LEVEL_DEFAULT   },

src/gfx/warning.cpp

@@ -17,6 +17,7 @@ Diagnostics<WarningLevel, WarningID> warnings = {
     },
     .warningFlags = {
         {"embedded",      LEVEL_EVERYTHING},
+        {"obsolete",      LEVEL_DEFAULT   },
         {"trim-nonempty", LEVEL_ALL       },
     },
     .paramWarnings = {},