Change cmake version from 3.9 to 3.5

No feature of cmake newer than 3.5 is used. Therefore, we can use
cmake 3.5, which is also standard in Ubuntu 16.04, whereas cmake 3.9
is non-standard.

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.9.0)
+cmake_minimum_required(VERSION 3.5.1)
 project(CARLA)
 
 include("Build/CMakeLists.txt.in")

Docs/how_to_build_on_linux.md

@@ -12,10 +12,6 @@ sudo apt-get install build-essential clang-5.0 lld-5.0 g++-7 ninja-build python
 pip install --user setuptools nose2
 ```
 
-Note that some dependencies require **CMake 3.9** or later installed in your
-machine, you can retrieve the latest version from the
-[CMake download page][cmakelink].
-
 To avoid compatibility issues between Unreal Engine and the CARLA dependencies,
 the best configuration is to compile everything with the same compiler version
 and C++ runtime library. We use clang 5.0 and LLVM's libc++. We recommend to

LibCarla/cmake/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.9.0)
+cmake_minimum_required(VERSION 3.5.1)
 project(libcarla)
 
 message(STATUS "Building ${PROJECT_NAME} version ${CARLA_VERSION}")

LibCarla/cmake/client/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.9.0)
+cmake_minimum_required(VERSION 3.5.1)
 project(libcarla-client)
 
 # Install rpclib.

LibCarla/cmake/server/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.9.0)
+cmake_minimum_required(VERSION 3.5.1)
 project(libcarla-server)
 
 # Install libc++ shared libraries.

LibCarla/cmake/test/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.9.0)
+cmake_minimum_required(VERSION 3.5.1)
 project(libcarla-unit-tests)
 
 file(GLOB_RECURSE libcarla_test_sources

Util/BuildTools/Setup.sh

@@ -149,6 +149,10 @@ else
 
   log "Building rpclib with libc++."
 
+  # rpclib does not use any cmake 3.9 feature. 
+  # As cmake 3.9 is not standard in Ubuntu 16.04, change cmake version to 3.5
+  sed -i s/"3.9.0"/"3.5.0"/g ${RPCLIB_BASENAME}-source/CMakeLists.txt
+
   mkdir -p ${RPCLIB_BASENAME}-libcxx-build
 
   pushd ${RPCLIB_BASENAME}-libcxx-build >/dev/null