Make compiler/optimizing/ symbols hidden.

Make symbols in compiler/optimizing hidden by a namespace
attribute. The unit intrinsic_objects.{h,cc} is excluded as
it is needed by dex2oat.

As the symbols are no longer exported, gtests are now linked
with the static version of the libartd-compiler library.

libart-compiler.so size:
  - before:
    arm: 2396152
    arm64: 3345280
  - after:
    arm: 2016176 (-371KiB, -15.9%)
    arm64: 2874480 (-460KiB, -14.1%)

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing --jit
Bug: 142365358
Change-Id: I1fb04a33351f53f00b389a1642e81a68e40912a8
diff --git a/compiler/optimizing/code_sinking.h b/compiler/optimizing/code_sinking.h
index 8eb3a52..14f62f2 100644
--- a/compiler/optimizing/code_sinking.h
+++ b/compiler/optimizing/code_sinking.h
@@ -17,10 +17,11 @@
 #ifndef ART_COMPILER_OPTIMIZING_CODE_SINKING_H_
 #define ART_COMPILER_OPTIMIZING_CODE_SINKING_H_
 
+#include "base/macros.h"
 #include "nodes.h"
 #include "optimization.h"
 
-namespace art {
+namespace art HIDDEN {
 
 /**
  * Optimization pass to move instructions into uncommon branches,