Add "memory" and "cc" to the clobbers of atomic instructions in ref.hh

The gcc docs say use "memory" if "your assembler instructions access memory in an unpredictable fashion". I don't know what that means, but linux adds "memory" for similar inlines. The gcc docs say use "cc" if "assembler instruction can alter the condition code register". I know what that means, but linux doesn't use it.

Add "memory" and "cc" to the clobbers of atomic instructions in ref.hh
992b264a · Silas Boyd-Wickizer · a8b456f0 · 992b264a
--- a/include/ref.hh
+++ b/include/ref.hh
@@ -52,7 +52,7 @@ public:
    // If references is 0 (i.e. ref_.count is 0xffffffff) a 32-bit 
    // increment will increases ref_.count to 0, but ref_.invalid
    // will remain unchanged.
-    asm volatile("lock; incl %0" : "+m" (ref_.count));
+    asm volatile("lock; incl %0" : "+m" (ref_.count) :: "memory", "cc");
  }

  inline bool tryinc() const {
@@ -64,7 +64,8 @@ public:
    unsigned char c;
    // If references is 1 (i.e. ref_.v is 0), a 64-bit decrement will
    // underflow ref_.invalid to 0xffffffff (and ref_.count to 0xffffffff).
-    asm volatile("lock; decq %0; sets %1" : "+m" (ref_.v), "=qm" (c));
+    asm volatile("lock; decq %0; sets %1" : "+m" (ref_.v), "=qm" (c) 
+                 :: "memory", "cc");
    if (c)
      onzero();
  }