Give TARGET_OUT_HEADERS to vendor modules

Many vendor modules are using headers that are copied to
$(TARGET_OUT_HEADERS)/some/path via LOCAL_COPY_HEADERS. In order to let
them use the headers via #include <some/path/header.h>,
$(TARGET_OUT_HEADERS) is again added to the system include path.

Bug: 63340459
Test: BOARD_VNDK_VERSION=current m -j gives less 'cannot find header'
errors.

Change-Id: I472e74533b437653c76dc416f7f4527c0e90750d
diff --git a/core/binary.mk b/core/binary.mk
index 61a8ef6..6b2bf71 100644
--- a/core/binary.mk
+++ b/core/binary.mk
@@ -523,6 +523,7 @@
 my_target_global_c_includes := \
     $($(LOCAL_2ND_ARCH_VAR_PREFIX)$(my_prefix)PROJECT_INCLUDES)
 my_target_global_c_system_includes := \
+    $(TARGET_OUT_HEADERS) \
     $($(LOCAL_2ND_ARCH_VAR_PREFIX)$(my_prefix)PROJECT_SYSTEM_INCLUDES)
 else ifdef LOCAL_SDK_VERSION
 my_target_global_c_includes :=