Remove uses of libcxx.mk.

This is a no-op.

Change-Id: Iecbcd5f6d818abbf98767a2e996c10f454b652e4

libbacktrace/Android.build.mk

@@ -68,9 +68,6 @@ ifeq ($(build_type),host)
   # Only build if host builds are supported.
   ifeq ($(build_host),true)
     LOCAL_CFLAGS += -Wno-extern-c-compat -fno-omit-frame-pointer
-    ifneq ($($(module)_libc++),)
-      include external/libcxx/libcxx.mk
-    endif
     include $(BUILD_HOST_$(build_target))
   endif
 endif

libprocessgroup/Android.mk

@@ -8,7 +8,6 @@ LOCAL_C_INCLUDES := $(LOCAL_PATH)/include
 LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)/include
 LOCAL_CFLAGS := -Wall -Werror
 LOCAL_REQUIRED_MODULE := processgroup_cleanup
-include external/libcxx/libcxx.mk
 include $(BUILD_SHARED_LIBRARY)
 
 include $(CLEAR_VARS)

libsync/tests/Android.mk

@@ -17,7 +17,6 @@
 LOCAL_PATH:= $(call my-dir)
 
 include $(CLEAR_VARS)
-include external/libcxx/libcxx.mk
 LOCAL_CLANG := true
 LOCAL_MODULE := sync-unit-tests
 LOCAL_ADDITIONAL_DEPENDENCIES := $(LOCAL_PATH)/Android.mk