Add support for enabling DCHECKs in release mode

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index e95b7edf75ce157918cae03ecd69ec7c208fdecb..18c19ecfda3ec1b7db6f85d7cec781fa7e4a200a 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -172,7 +172,7 @@ class PredictableCodeSizeScope {
 // Enable a specified feature within a scope.
 class CpuFeatureScope BASE_EMBEDDED {
  public:
-#ifdef DEBUG
+#if DCHECK_IS_ON
   CpuFeatureScope(AssemblerBase* assembler, CpuFeature f);
   ~CpuFeatureScope();
 
@@ -596,7 +596,7 @@ class RelocInfo {
   // debugger.
   INLINE(bool IsPatchedDebugBreakSlotSequence());
 
-#ifdef DEBUG
+#if DCHECK_IS_ON
   // Check whether the given code contains relocation information that
   // either is position-relative or movable by the garbage collector.
   static bool RequiresRelocation(const CodeDesc& desc);