Add missing FindLibffi.cmake

PiperOrigin-RevId: 257378727
Change-Id: Ib1a6b6734a56280ff5dc9cc75380fcb9b9f51197

cmake/FindLibffi.cmake

@@ -0,0 +1,34 @@
+# Copyright 2019 Google LLC. 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.
+
+# On Debian, install libffi-dev to use this module.
+
+find_path(libffi_INCLUDE_DIR ffitarget.h)
+# Look for static library only.
+find_library(libffi_LIBRARY libffi.a)
+mark_as_advanced(libffi_INCLUDE_DIR libffi_LIBRARY)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(libffi
+  REQUIRED_VARS libffi_LIBRARY libffi_INCLUDE_DIR
+)
+
+if(libffi_FOUND AND NOT TARGET libffi::libffi)
+  add_library(libffi::libffi UNKNOWN IMPORTED)
+  set_target_properties(libffi::libffi PROPERTIES
+    IMPORTED_LINK_INTERFACE_LANGUAGES "C"
+    IMPORTED_LOCATION "${libffi_LIBRARY}"
+    INTERFACE_INCLUDE_DIRECTORIES "${libffi_INCLUDE_DIR}"
+  )
+endif()