Optimizing/X86: PC-relative dex cache array addressing.

Add PC-relative dex cache array addressing for X86 and use
it for better invoke-static/-direct dispatch. Also delay
the initialization to the PC-relative base until needed.

Change-Id: Ib8634d5edce4920cd70172fd13211809cf6948d1
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index ce92470..5188e11 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -208,6 +208,7 @@
 void CodeGenerator::GenerateSlowPaths() {
   size_t code_start = 0;
   for (SlowPathCode* slow_path : slow_paths_) {
+    current_slow_path_ = slow_path;
     if (disasm_info_ != nullptr) {
       code_start = GetAssembler()->CodeSize();
     }
@@ -216,6 +217,7 @@
       disasm_info_->AddSlowPathInterval(slow_path, code_start, GetAssembler()->CodeSize());
     }
   }
+  current_slow_path_ = nullptr;
 }
 
 void CodeGenerator::CompileInternal(CodeAllocator* allocator, bool is_baseline) {