Simplify CMake Policies

Per LMMS#6758 (comment)

CMakeLists.txt

@@ -6,17 +6,13 @@ SET(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake/modules" ${CMAKE_MODULE_PATH})
 SET(LMMS_BINARY_DIR ${CMAKE_BINARY_DIR})
 SET(LMMS_SOURCE_DIR ${CMAKE_SOURCE_DIR})
 
-IF(COMMAND CMAKE_POLICY)
-	CMAKE_POLICY(SET CMP0005 NEW)
-	CMAKE_POLICY(SET CMP0003 NEW)
-	IF (CMAKE_MAJOR_VERSION GREATER 2)
-		CMAKE_POLICY(SET CMP0026 NEW)
-		CMAKE_POLICY(SET CMP0045 NEW)
-		CMAKE_POLICY(SET CMP0050 OLD)
-	ENDIF()
-	CMAKE_POLICY(SET CMP0020 NEW)
-	CMAKE_POLICY(SET CMP0057 NEW)
-ENDIF(COMMAND CMAKE_POLICY)
+CMAKE_POLICY(SET CMP0005 NEW)	# Preprocessor definition values are now escaped automatically
+CMAKE_POLICY(SET CMP0003 NEW)   # Libraries linked via full path no longer produce linker search paths.
+CMAKE_POLICY(SET CMP0026 NEW)	# Disallow use of the LOCATION property for build targets.
+CMAKE_POLICY(SET CMP0045 NEW)   # Error on non-existent target in get_target_property.
+CMAKE_POLICY(SET CMP0050 OLD)   # Disallow add_custom_command SOURCE signatures.
+CMAKE_POLICY(SET CMP0020 NEW)	# Automatically link Qt executables to qtmain target on Windows.
+CMAKE_POLICY(SET CMP0057 NEW)	# Support new if() IN_LIST operator.
 
 
 # Import of windows.h breaks min()/max()