x86_64 build fix: declare gc_alloc_block_sync

diff --git a/includes/rts/storage/MBlock.h b/includes/rts/storage/MBlock.h
index 03396c1..fb5289d 100644 (file)
--- a/includes/rts/storage/MBlock.h
+++ b/includes/rts/storage/MBlock.h
@@ -143,6 +143,10 @@ typedef struct {
 
 extern lnat mpc_misses;
 
+#ifdef THREADED_RTS
+extern SpinLock gc_alloc_block_sync;
+#endif
+
 StgBool HEAP_ALLOCED_miss(StgWord mblock, void *p);
 
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