Reland "Remove V8_HOST_CAN_READ_UNALIGNED and its uses."

src/regexp-macro-assembler-irregexp.h

Index: src/regexp-macro-assembler-irregexp.h
diff --git a/src/regexp-macro-assembler-irregexp.h b/src/regexp-macro-assembler-irregexp.h
index cdfb46ad15e05df38616ebed8398d8c0cbd5737c..b192c22b6f020b6cc1cb7fef941245e49c957a7f 100644
--- a/src/regexp-macro-assembler-irregexp.h
+++ b/src/regexp-macro-assembler-irregexp.h
@@ -31,6 +31,7 @@ class RegExpMacroAssemblerIrregexp: public RegExpMacroAssembler {
   virtual ~RegExpMacroAssemblerIrregexp();
   // The byte-code interpreter checks on each push anyway.
   virtual int stack_limit_slack() { return 1; }
+  virtual bool CanReadUnaligned() { return false; }
   virtual void Bind(Label* label);
   virtual void AdvanceCurrentPosition(int by);  // Signed cp change.
   virtual void PopCurrentPosition();