increase minimal version requirement to 3.5, call before project

Future cmake will no longer support features before version 3.5
Also `cmake_minimum_required` must be called before `project`

CMakeLists.txt

@@ -1,17 +1,18 @@
-cmake_minimum_required(VERSION 3.4.3)
+if(WIN32)
+  # We need cmake to support exporting of symbols not only from libraries but
+  # from executables too. This way cling can find symbols from its own
+  # executable during runtime.
+  cmake_minimum_required(VERSION 3.6.2)
+else(WIN32)
+  # support of earlier cmake versions will be removed soon
+  cmake_minimum_required(VERSION 3.5)
+endif(WIN32)
 
 # If we are not building as a part of LLVM, build Cling as an
 # standalone project, using LLVM as an external library:
 if( CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR )
   project(Cling)
 
-  if(WIN32)
-    # We need cmake to support exporting of symbols not only from libraries but
-    # from executables too. This way cling can find symbols from its own
-    # executable during runtime.
-    cmake_minimum_required(VERSION 3.6.2)
-  endif(WIN32)
-
   # Rely on llvm-config.
   set(CONFIG_OUTPUT)
   find_program(LLVM_CONFIG "llvm-config")