Revert "Merge pull request duckdb#9364 from taniabogatsch/increase-cm…

…ake-version"

This reverts commit 2646836, reversing
changes made to 7127284.

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 2.8.12)
 
 if(POLICY CMP0026)
   cmake_policy(SET CMP0026 NEW)
@@ -22,7 +22,12 @@ find_package(Threads REQUIRED)
 
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
-set (CMAKE_CXX_STANDARD 11)
+if (CMAKE_VERSION VERSION_LESS "3.1")
+    set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+else ()
+  set (CMAKE_CXX_STANDARD 11)
+endif ()
+
 
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
@@ -624,7 +629,12 @@ function(link_extension_libraries LIBRARY)
 endfunction()
 
 function(link_threads LIBRARY)
+  if (CMAKE_VERSION VERSION_LESS "3.1")
+    target_link_libraries(${LIBRARY} pthread)
+
+  else()
     target_link_libraries(${LIBRARY} Threads::Threads)
+  endif()
 endfunction()
 
 function(build_loadable_extension_directory NAME OUTPUT_DIRECTORY PARAMETERS)
@@ -1084,7 +1094,7 @@ if (NOT "${LOCAL_EXTENSION_REPO}" STREQUAL "")
   message(STATUS "Extensions will be deployed to: ${LOCAL_EXTENSION_REPO}")
 endif()
 
-if (NOT EXTENSION_CONFIG_BUILD )
+if (CMAKE_VERSION VERSION_GREATER "3.0" AND NOT EXTENSION_CONFIG_BUILD ) # this does not work with 2.8
 # Write the export set for build and install tree
 install(EXPORT "${DUCKDB_EXPORT_SET}" DESTINATION "${INSTALL_CMAKE_DIR}")
 export(EXPORT "${DUCKDB_EXPORT_SET}"

extension/parquet/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 2.8.12)
 
 project(ParquetExtension)
 

third_party/imdb/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 2.8.12)
 
 if(POLICY CMP0063)
     cmake_policy(SET CMP0063 NEW)

third_party/libpg_query/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 2.8.12)
 
 project(duckdb_pg_query CXX C)
 if(POLICY CMP0063)

third_party/re2/CMakeLists.txt

@@ -1,7 +1,8 @@
 # Copyright 2015 The RE2 Authors.  All Rights Reserved. Use of this source code
 # is governed by a BSD-style license that can be found in the LICENSE file.
 
-cmake_minimum_required(VERSION 3.5)
+# Old enough to support Ubuntu Trusty.
+cmake_minimum_required(VERSION 2.8.12)
 
 if(POLICY CMP0048)
   cmake_policy(SET CMP0048 NEW)