https://bugs.gentoo.org/740382
--- a/src/sh4/sh4trans.h
+++ b/src/sh4/sh4trans.h
@@ -130,7 +130,7 @@ gboolean sh4_translate_flush_cache( void );
  * Either returns immediately (to skip the breakpoint), or aborts the current
  * cycle and never returns.
  */
-void FASTCALL sh4_translate_breakpoint_hit( sh4vma_t pc );
+extern void FASTCALL sh4_translate_breakpoint_hit( sh4vma_t pc );
 
 #ifdef __cplusplus
 }