Add CMake finder for downstream projects

Change-Id: Ife37f7ead18ee28f8f4fd5e29caeee5e825defd4

CMake/FindFlatBuffers.cmake

+# Copyright 2014 Stefan.Eilemann@epfl.ch
+# Copyright 2014 Google Inc. All rights reserved.
+#
+# 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.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Find the flatbuffers schema compiler
+#
+# Output Variables:
+# * FLATBUFFERS_FLATC_EXECUTABLE the flatc compiler executable
+# * FLATBUFFERS_FOUND
+#
+# Provides:
+# * FLATBUFFERS_GENERATE_C_HEADERS(Name <files>) creates the C++ headers
+#   for the given flatbuffer schema files.
+#   Returns the header files in ${Name}_OUTPUTS
+
+find_program(FLATBUFFERS_FLATC_EXECUTABLE NAMES flatc)
+find_path(FLATBUFFERS_INCLUDE_DIR NAMES flatbuffers/flatbuffers.h)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(flatbuffers
+  DEFAULT_MSG FLATBUFFERS_FLATC_EXECUTABLE FLATBUFFERS_INCLUDE_DIR)
+
+if(FLATBUFFERS_FOUND)
+  function(FLATBUFFERS_GENERATE_C_HEADERS Name)
+    set(FLATC_OUTPUTS)
+    foreach(FILE ${ARGN})
+      get_filename_component(FLATC_OUTPUT ${FILE} NAME_WE)
+      set(FLATC_OUTPUT
+        "${CMAKE_CURRENT_BINARY_DIR}/${FLATC_OUTPUT}_generated.h")
+      list(APPEND FLATC_OUTPUTS ${FLATC_OUTPUT})
+
+      add_custom_command(OUTPUT ${FLATC_OUTPUT}
+        COMMAND ${FLATBUFFERS_FLATC_EXECUTABLE}
+        ARGS -c -o "${CMAKE_CURRENT_BINARY_DIR}/" ${FILE}
+        COMMENT "Building C++ header for ${FILE}"
+        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
+    endforeach()
+    set(${Name}_OUTPUTS ${FLATC_OUTPUTS} PARENT_SCOPE)
+  endfunction()
+
+  set(FLATBUFFERS_INCLUDE_DIRS ${FLATBUFFERS_INCLUDE_DIR})
+  include_directories(${CMAKE_BINARY_DIR})
+else()
+  set(FLATBUFFERS_INCLUDE_DIR)
+endif()