Fix building against GCC 10

* GCC 10 defaults to `-fno-common`, which makes C behave
  more like C++ in that you can only ever have one definition
  of an object per executable.

Author: SoapGentoo

rle.h

@@ -30,7 +30,7 @@ extern "C" {
  *** 43+3 codec ***
  ******************/
 
-const uint8_t rle_auxtab[8];
+extern const uint8_t rle_auxtab[8];
 
 #define RLE_MIN_SPACE 18
 #define rle_nptr(block) ((uint16_t*)(block))