ART: Fix CFI test wrt/ PIC

PIC boot images can't be loaded with dlopen, as their base is zero,
but we have an expectant address. Turn off in-process unwinding
in 137-cfi by checking the boot image oat file type.

Keep a non-owned referenced to the oat file in image space to simplify
access.

Change-Id: Ia2b525f9b2ecbc80b433f09e04ebece4cb6f2d2b
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index dc8a3d1..c4d978f 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -808,18 +808,11 @@
 }
 
 const OatFile* ClassLinker::GetBootOatFile() {
-  // To grab the boot oat, look at the dex files in the boot classpath. Any of those is fine, as
-  // they were all compiled into the same oat file. So grab the first one, which is guaranteed to
-  // exist if the boot class-path isn't empty.
-  if (boot_class_path_.empty()) {
+  gc::space::ImageSpace* image_space = Runtime::Current()->GetHeap()->GetImageSpace();
+  if (image_space == nullptr) {
     return nullptr;
   }
-  const DexFile* boot_dex_file = boot_class_path_[0];
-  // Is it from an oat file?
-  if (boot_dex_file->GetOatDexFile() != nullptr) {
-    return boot_dex_file->GetOatDexFile()->GetOatFile();
-  }
-  return nullptr;
+  return image_space->GetOatFile();
 }
 
 const OatFile* ClassLinker::GetPrimaryOatFile() {