Move ObjC compilation actions for J2ObjC-translated code from binary level to the edges (J2ObjcAspect and J2ObjcProtoAspect).

RELNOTES[INC]:
ObjC compile actions for J2ObjC-translated code now only has access to headers from the java deps of the associated original java rule.
These compile actions no longer takes the compiler options specified in "copts" attribute on objc_binary/ios_test rules.
J2ObjC dead code removal (enabled through flag "--j2objc_dead_code_removal") now happens *after* ObjC compilation.

--
MOS_MIGRATED_REVID=113910545
diff --git a/tools/objc/BUILD b/tools/objc/BUILD
index b9eb66b..4b6b56c 100644
--- a/tools/objc/BUILD
+++ b/tools/objc/BUILD
@@ -119,3 +119,8 @@
     name = "j2objc_dead_code_pruner",
     srcs = ["j2objc_dead_code_pruner.py"],
 )
+
+objc_library(
+    name = "dummy_lib",
+    srcs = ["dummy.c"],
+)