Add hybrid assembler concept to ARM assembler.

src/IceAssembler.h

Index: src/IceAssembler.h
diff --git a/src/IceAssembler.h b/src/IceAssembler.h
index 2f5a505363f329f5b544d6378032c35ab155bca6..c3fe9c394b3f6fb2fa0502632b19e1e72d684243 100644
--- a/src/IceAssembler.h
+++ b/src/IceAssembler.h
@@ -174,6 +174,9 @@ public:
   /// Create and track a fixup in the current function.
   AssemblerFixup *createFixup(FixupKind Kind, const Constant *Value);
 
+  /// Installs a created fixup, after it has been allocated.
+  void installFixup(AssemblerFixup *F);
+
   const FixupRefList &fixups() const { return Fixups; }
 
   void setSize(intptr_t NewSize) {
@@ -268,6 +271,9 @@ public:
   // Return a view of all the bytes of code for the current function.
   llvm::StringRef getBufferView() const;
 
+  /// Emit a fixup at the current location.
+  void emitFixup(AssemblerFixup *Fixup) { Buffer.emitFixup(Fixup); }
+
   const FixupRefList &fixups() const { return Buffer.fixups(); }
 
   AssemblerFixup *createFixup(FixupKind Kind, const Constant *Value) {
@@ -291,6 +297,9 @@ protected:
   explicit Assembler(AssemblerKind Kind, GlobalContext *Ctx)
       : Kind(Kind), Allocator(), Ctx(Ctx), Buffer(*this) {}
 
+  /// Installs a created fixup, after it has been allocated.
+  void installFixup(AssemblerFixup *F) { Buffer.installFixup(F); }
+
 private:
   const AssemblerKind Kind;