Fix build with -fno-common

Index: src/display.h
--- src/display.h.orig
+++ src/display.h
@@ -73,7 +73,7 @@ enum {
     C_MAGENTA,
     C_CYAN,
     NUM_COLORS,
-} colors_available;
+};
 
 
 
@@ -89,7 +89,7 @@ enum {
     MSDL_DBG   = 3,     /* debug      */
 
     MSDL_ERR = MSDL_NOR | MSDL_OUTPUT_ERR,
-} display_flags;
+};
 
 
 struct displayinfo_t {