Move back the boot image to debuggable.

Full frame deoptimization is broken with it.

Partial revert of https://android-review.googlesource.com/#/c/201383/

Change-Id: I7a402d79b0882f81987e56869551840da7d553e0
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index d9a2f30..f25d748 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -698,6 +698,12 @@
       Usage("Can't have both --image and (--app-image-fd or --app-image-file)");
     }
 
+    if (IsBootImage()) {
+      // We need the boot image to always be debuggable.
+      // TODO: Remove this once we better deal with full frame deoptimization.
+      compiler_options_->debuggable_ = true;
+    }
+
     if (oat_filenames_.empty() && oat_fd_ == -1) {
       Usage("Output must be supplied with either --oat-file or --oat-fd");
     }