Bug 1543034 - ifdef traceMagic to avoid warning about unused variable. r=tcampbell

Differential Revision: https://phabricator.services.mozilla.com/D26766

--HG--
extra : moz-landing-system : lando

js/src/jit/BaselineIC.h

@@ -223,11 +223,13 @@ class ICEntry {
   // The PC of this IC's bytecode op within the JSScript.
   uint32_t pcOffset_;
 
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
 #ifdef JS_64BIT
   // On 64-bit architectures, we have 32 bits of alignment padding.
   // We fill it with a magic value, and check that value when tracing.
   static const uint32_t EXPECTED_TRACE_MAGIC = 0xdeaddead;
   uint32_t traceMagic_ = EXPECTED_TRACE_MAGIC;
+#endif
 #endif
 
  public: