Revert "Revert "Store resolved Strings for AOT code in .bss.""

Fixed oat_test to keep dex files alive. Fixed mips build.
Rewritten the .bss GC root visiting and added write barrier
to the artResolveStringFromCode().

Test: build aosp_mips-eng
Test: m ART_DEFAULT_GC_TYPE=SS test-art-target-host-gtest-oat_test
Test: Run ART test suite on host and Nexus 9.
Bug: 20323084
Bug: 30627598

This reverts commit 5f926055cb88089d8ca27243f35a9dfd89d981f0.

Change-Id: I07fa2278d82b8eb64964c9a4b66cb93726ccda6b
diff --git a/compiler/optimizing/pc_relative_fixups_mips.cc b/compiler/optimizing/pc_relative_fixups_mips.cc
index 6006e6c..82feb95 100644
--- a/compiler/optimizing/pc_relative_fixups_mips.cc
+++ b/compiler/optimizing/pc_relative_fixups_mips.cc
@@ -83,6 +83,7 @@
       case HLoadString::LoadKind::kBootImageLinkTimeAddress:
       case HLoadString::LoadKind::kBootImageAddress:
       case HLoadString::LoadKind::kBootImageLinkTimePcRelative:
+      case HLoadString::LoadKind::kBssEntry:
         // Add a base register for PC-relative literals on R2.
         InitializePCRelativeBasePointer();
         load_string->AddSpecialInput(base_);