chore: import upstream snapshot with attribution

cmake/FindGFLAGS.cmake

@@ -0,0 +1,41 @@
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You 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.
+
+set(_gflags_ORIG_CMAKE_FIND_LIBRARY_SUFFIXES ${CMAKE_FIND_LIBRARY_SUFFIXES})
+
+find_path(GFLAGS_INCLUDE_PATH gflags/gflags.h)
+
+if (GFLAGS_STATIC)
+  if (WIN32)
+    set(CMAKE_FIND_LIBRARY_SUFFIXES .lib ${CMAKE_FIND_LIBRARY_SUFFIXES})
+  else (WIN32)
+    set(CMAKE_FIND_LIBRARY_SUFFIXES .a ${CMAKE_FIND_LIBRARY_SUFFIXES})
+  endif (WIN32)
+endif (GFLAGS_STATIC)
+find_library(GFLAGS_LIBRARY NAMES gflags libgflags)
+if(GFLAGS_INCLUDE_PATH AND GFLAGS_LIBRARY)
+  set(GFLAGS_FOUND TRUE)
+endif(GFLAGS_INCLUDE_PATH AND GFLAGS_LIBRARY)
+if(GFLAGS_FOUND)
+  if(NOT GFLAGS_FIND_QUIETLY)
+    message(STATUS "Found gflags: ${GFLAGS_LIBRARY}")
+  endif(NOT GFLAGS_FIND_QUIETLY)
+else(GFLAGS_FOUND)
+  if(GFLAGS_FIND_REQUIRED)
+    message(FATAL_ERROR "Could not find gflags library.")
+  endif(GFLAGS_FIND_REQUIRED)
+endif(GFLAGS_FOUND)
+
+set(CMAKE_FIND_LIBRARY_SUFFIXES ${_gflags_ORIG_CMAKE_FIND_LIBRARY_SUFFIXES})