Refactor linker files from compiler/ to dex2oat/.

This shifts some code from the libart-compiler.so to dex2oat
and reduces memory needed for JIT. We also avoid loading the
libart-dexlayout.so for JIT but the memory savings are
minimal (one shared clean page, two shared dirty pages and
some per-app kernel mmap data) as the code has never been
needed in memory by JIT.

aosp_angler-userdebug file sizes (stripped):
  lib64/libart-compiler.so: 2989112 -> 2671888 (-310KiB)
  lib/libart-compiler.so: 2160816 -> 1939276 (-216KiB)
  bin/dex2oat: 141868 -> 368808 (+222KiB)
LOAD/executable elf mapping sizes:
  lib64/libart-compiler.so: 2866308 -> 2555500 (-304KiB)
  lib/libart-compiler.so: 2050960 -> 1834836 (-211KiB)
  bin/dex2oat: 129316 -> 345916 (+212KiB)

Test: m test-art-host-gtest
Test: testrunner.py --host
Test: cd art/; mma; cd -
Change-Id: If62f02847a6cbb208eaf7e1f3e91af4663fa4a5f
diff --git a/runtime/class_table.h b/runtime/class_table.h
index 0ffe93e..744c010 100644
--- a/runtime/class_table.h
+++ b/runtime/class_table.h
@@ -32,6 +32,14 @@
 
 class OatFile;
 
+namespace linker {
+class ImageWriter;
+}  // namespace linker
+
+namespace linker {
+class OatWriter;
+}  // namespace linker
+
 namespace mirror {
   class Class;
   class ClassLoader;
@@ -286,8 +294,8 @@
   // Keep track of oat files with GC roots associated with dex caches in `strong_roots_`.
   std::vector<const OatFile*> oat_files_ GUARDED_BY(lock_);
 
-  friend class ImageWriter;  // for InsertWithoutLocks.
-  friend class OatWriter;  // for boot class TableSlot address lookup.
+  friend class linker::ImageWriter;  // for InsertWithoutLocks.
+  friend class linker::OatWriter;  // for boot class TableSlot address lookup.
 };
 
 }  // namespace art