build: allow yamlcpp to be compiled statically optionally

Co-Authored-By: Leonardo Di Donato <leodidonato@gmail.com>
Signed-off-by: Lorenzo Fontana <lo@linux.com>

cmake/modules/FindYamlCpp.cmake

@@ -0,0 +1,38 @@
+#
+# Copyright (C) 2019 The Falco Authors.
+#
+# 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.
+#
+
+option(
+  BUILD_STATIC_YAMLCPP
+  "Build a static version of yaml-cpp (useful for building in Operating Systems that don't have the yaml-cpp package)"
+  OFF)
+
+if(NOT BUILD_STATIC_YAMLCPP)
+  find_path(YAMLCPP_INCLUDE_DIR NAMES yaml-cpp/yaml.h)
+  find_library(YAMLCPP_LIB NAMES yaml-cpp)
+  if(YAMLCPP_INCLUDE_DIR AND YAMLCPP_LIB)
+    message(STATUS "Found yamlcpp: include: ${YAMLCPP_INCLUDE_DIR}, lib: ${YAMLCPP_LIB}")
+  else()
+    message(FATAL_ERROR "Couldn't find system yamlcpp")
+  endif()
+else()
+  set(YAMLCPP_SRC "${PROJECT_BINARY_DIR}/yamlcpp-prefix/src/yamlcpp")
+  message(STATUS "Using bundled yaml-cpp in '${YAMLCPP_SRC}'")
+  set(YAMLCPP_LIB "${YAMLCPP_SRC}/libyaml-cpp.a")
+  set(YAMLCPP_INCLUDE_DIR "${YAMLCPP_SRC}/include")
+  ExternalProject_Add(
+    yamlcpp
+    URL "https://github.com/jbeder/yaml-cpp/archive/yaml-cpp-0.6.2.tar.gz"
+    URL_MD5 "5b943e9af0060d0811148b037449ef82"
+    BUILD_IN_SOURCE 1
+    INSTALL_COMMAND "")
+endif()