Allow globally disabling the relocation packer.

The relocation packer is part of prebuilts/misc, and pulling that
repository into the manifest requires pulling in a lot of other things
not needed by the simpler builds (like the clang toolchain manifest).

Bug: http://b/17441393
Change-Id: If4a94804fc1a3f81215b840247f8e332d0b510c1
diff --git a/core/prebuilt_internal.mk b/core/prebuilt_internal.mk
index 505bd45..3af7101 100644
--- a/core/prebuilt_internal.mk
+++ b/core/prebuilt_internal.mk
@@ -48,6 +48,10 @@
     # Do not pack relocations by default
     LOCAL_PACK_MODULE_RELOCATIONS := false
   endif
+
+  ifeq ($(DISABLE_RELOCATION_PACKER),true)
+    LOCAL_PACK_MODULE_RELOCATIONS := false
+  endif
 endif
 
 ifneq ($(filter STATIC_LIBRARIES SHARED_LIBRARIES,$(LOCAL_MODULE_CLASS)),)