Set CMake policy CMP0057 to NEW.

This is necessary for CheckLinkerFlag with CMake 3.18.

Add includes for other checks that are used in TDEMacros.
The initialization of the TDEMacros moved to the beginning.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>

modules/TDEMacros.cmake

@@ -15,10 +15,6 @@
 #
 #################################################
 
-include( CheckCXXCompilerFlag )
-include( CheckLinkerFlag OPTIONAL )
-include( TDEVersion )
-
 
 #################################################
 #####
@@ -67,6 +63,28 @@ if( NOT TDE_CMAKE_ROOT )
 endif()
 
 
+#################################################
+#####
+##### set necessary CMake policies
+
+if( POLICY CMP0057 )
+  # necessary for CheckLinkerFlag
+  cmake_policy( SET CMP0057 NEW )
+endif()
+
+
+#################################################
+#####
+##### necessary includes
+
+include( CheckCXXCompilerFlag )
+include( CheckCXXSourceCompiles )
+include( CheckLinkerFlag OPTIONAL )
+include( CheckSymbolExists )
+include( CheckTypeSize )
+include( TDEVersion )
+
+
 #################################################
 #####
 ##### tde_message_author_warning