android编译单独模块时异常提示

lqm@lqm:~/android_gingerbread$ make ledtestapp
============================================
PLATFORM_VERSION_CODENAME=REL
PLATFORM_VERSION=2.3.1
TARGET_PRODUCT=generic
TARGET_BUILD_VARIANT=eng
TARGET_SIMULATOR=
TARGET_BUILD_TYPE=release
TARGET_BUILD_APPS=
TARGET_ARCH=arm
HOST_ARCH=x86
HOST_OS=linux
HOST_BUILD_TYPE=release
BUILD_ID=GINGERBREAD
============================================
build/core/base_rules.mk:74: *** Module name: ledtestapp
build/core/base_rules.mk:75: *** Makefile location: external/led
build/core/base_rules.mk:76: * 
build/core/base_rules.mk:77: * Each module must use a LOCAL_MODULE_TAGS in its
build/core/base_rules.mk:78: * Android.mk. Possible tags declared by a module:
build/core/base_rules.mk:79: * 
build/core/base_rules.mk:80: *     optional, debug, eng, tests, samples
build/core/base_rules.mk:81: * 
build/core/base_rules.mk:82: * If the module is expected to be in all builds
build/core/base_rules.mk:83: * of a product, then it should use the
build/core/base_rules.mk:84: * "optional" tag: 
build/core/base_rules.mk:85: * 
build/core/base_rules.mk:86: *    Add "LOCAL_MODULE_TAGS := optional" in the
build/core/base_rules.mk:87: *    Android.mk for the affected module, and add
build/core/base_rules.mk:88: *    the LOCAL_MODULE value for that component
build/core/base_rules.mk:89: *    into the PRODUCT_PACKAGES section of product
build/core/base_rules.mk:90: *    makefile(s) where it's necessary, if
build/core/base_rules.mk:91: *    appropriate.
build/core/base_rules.mk:92: * 
build/core/base_rules.mk:93: * If the component should be in EVERY build of ALL
build/core/base_rules.mk:94: * products, then add its LOCAL_MODULE value to the
build/core/base_rules.mk:95: * PRODUCT_PACKAGES section of
build/core/base_rules.mk:96: * build/target/product/core.mk
build/core/base_rules.mk:97: * 
build/core/base_rules.mk:98: *** user tag detected on new module - user tags are only supported on legacy modules。 停止

解决办法；

add LOCAL_MODULE_TAGS := optional in Android.mk where the error happens