Refactor RelativePatcher out of OatWriter.

Move the relative patcher classes to compiler/linker/ and
compiler/linker/<arch>/ . Refactor them to avoid OatWriter
dependency so that they can be unit tested. Add tests for
x86 and x86-64.

Change-Id: I1b42baa9fc431378e4cce1399bec590c5b5a409f
diff --git a/build/Android.gtest.mk b/build/Android.gtest.mk
index 1a4c30c..58a3290 100644
--- a/build/Android.gtest.mk
+++ b/build/Android.gtest.mk
@@ -193,6 +193,8 @@
   compiler/elf_writer_test.cc \
   compiler/image_test.cc \
   compiler/jni/jni_compiler_test.cc \
+  compiler/linker/x86/relative_patcher_x86_test.cc \
+  compiler/linker/x86_64/relative_patcher_x86_64_test.cc \
   compiler/oat_test.cc \
   compiler/optimizing/bounds_check_elimination_test.cc \
   compiler/optimizing/codegen_test.cc \