[PATCH] mem.c: declare file-local variables as 'static'

["Jun T." <takimoto-j@xxxxxxxxxxxxxxxxx>]

Just for consistency (and silence warnings).

# Or the 'static' is intentionally omitted?

diff --git a/Src/mem.c b/Src/mem.c
index e31145e..021dad5 100644
--- a/Src/mem.c
+++ b/Src/mem.c
@@ -157,13 +157,13 @@ mod_export Heapid last_heap_id;
  * Assumes old_heaps() will come along and restore it later
  * (outputs an error if old_heaps() is called out of sequence).
  */
-LinkList heaps_saved;
+static LinkList heaps_saved;
 
 /*
  * Debugging verbosity.  This must be set from a debugger.
  * An 'or' of bits from the enum heap_debug_verbosity.
  */
-volatile int heap_debug_verbosity;
+static volatile int heap_debug_verbosity;
 
 /*
  * Generate a heap identifier that's unique up to unsigned integer wrap.