Add GLOBAL option for external library targets

So that they can be found when paddle is built as a add_subdirectory project in another project.

cmake/external/gflags.cmake

 # Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
-# 
+#
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
-# 
+#
 # http://www.apache.org/licenses/LICENSE-2.0
-# 
+#
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -44,7 +44,7 @@ ExternalProject_Add(
                      -DCMAKE_BUILD_TYPE:STRING=Release
 )
 
-ADD_LIBRARY(gflags STATIC IMPORTED)
+ADD_LIBRARY(gflags STATIC IMPORTED GLOBAL)
 SET_PROPERTY(TARGET gflags PROPERTY IMPORTED_LOCATION ${GFLAGS_LIBRARIES})
 ADD_DEPENDENCIES(gflags extern_gflags)
 

cmake/external/glog.cmake

@@ -48,7 +48,7 @@ ExternalProject_Add(
                      -DCMAKE_BUILD_TYPE:STRING=Release
 )
 
-ADD_LIBRARY(glog STATIC IMPORTED)
+ADD_LIBRARY(glog STATIC IMPORTED GLOBAL)
 SET_PROPERTY(TARGET glog PROPERTY IMPORTED_LOCATION ${GLOG_LIBRARIES})
 ADD_DEPENDENCIES(glog extern_glog)
 

cmake/external/gtest.cmake

 # Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
-# 
+#
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
-# 
+#
 # http://www.apache.org/licenses/LICENSE-2.0
-# 
+#
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -56,11 +56,11 @@ IF(WITH_TESTING)
                          -DCMAKE_BUILD_TYPE:STRING=Release
     )
 
-    ADD_LIBRARY(gtest STATIC IMPORTED)
+    ADD_LIBRARY(gtest STATIC IMPORTED GLOBAL)
     SET_PROPERTY(TARGET gtest PROPERTY IMPORTED_LOCATION ${GTEST_LIBRARIES})
     ADD_DEPENDENCIES(gtest extern_gtest)
 
-    ADD_LIBRARY(gtest_main STATIC IMPORTED)
+    ADD_LIBRARY(gtest_main STATIC IMPORTED GLOBAL)
     SET_PROPERTY(TARGET gtest_main PROPERTY IMPORTED_LOCATION ${GTEST_MAIN_LIBRARIES})
     ADD_DEPENDENCIES(gtest_main extern_gtest)
 

cmake/external/warpctc.cmake

 # Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
-# 
+#
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
-# 
+#
 # http://www.apache.org/licenses/LICENSE-2.0
-# 
+#
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -65,7 +65,7 @@ ExternalProject_Add(
                      -DCMAKE_INSTALL_PREFIX:PATH=${WARPCTC_INSTALL_DIR}
 )
 
-ADD_LIBRARY(warpctc STATIC IMPORTED)
+ADD_LIBRARY(warpctc STATIC IMPORTED GLOBAL)
 SET_PROPERTY(TARGET warpctc PROPERTY IMPORTED_LOCATION ${WARPCTC_LIBRARIES})
 ADD_DEPENDENCIES(warpctc extern_warpctc)