Consolidate and simplify CMAKE_POLICY entries (#6780)

Simplify CMake Policies
Per https://github.com/LMMS/lmms/pull/6758#discussion_r1271346366

CMakeLists.txt

@@ -6,18 +6,7 @@ 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 Section
 
 # Import of windows.h breaks min()/max()
 ADD_DEFINITIONS(-DNOMINMAX)

cmake/modules/DefineInstallVar.cmake

@@ -24,7 +24,7 @@ function(DEFINE_INSTALL_VAR)
         endif()
     else()
         if(VAR_GENERATOR_EXPRESSION)
-            cmake_policy(SET CMP0087 NEW)
+            cmake_policy(SET CMP0087 NEW) # install(CODE) and install(SCRIPT) support generator expressions.
         endif()
         install(CODE "set(\"${VAR_NAME}\" \"${VAR_CONTENT}\")")
     endif()

cmake/modules/InstallDependencies.cmake

@@ -1,8 +1,8 @@
 include(GetPrerequisites)
 include(CMakeParseArguments)
 
-CMAKE_POLICY(SET CMP0011 NEW)
-CMAKE_POLICY(SET CMP0057 NEW)
+# Project's cmake_minimum_required doesn't always propagate
+cmake_policy(SET CMP0057 NEW) # Support new if() IN_LIST operator.
 
 function(make_absolute var)
 	get_filename_component(abs "${${var}}" ABSOLUTE BASE_DIR "${CMAKE_INSTALL_PREFIX}")

plugins/CarlaBase/CMakeLists.txt

@@ -1,11 +1,3 @@
-# For MacOS, use "OLD" RPATH install_name behavior
-# This can be changed to "NEW" safely if install_apple.sh.in
-# is updated to relink libcarlabase.dylib.  MacOS 10.8 uses
-# cmake 3.9.6, so this can be done at any time.
-IF(NOT CMAKE_VERSION VERSION_LESS 3.9)
-  CMAKE_POLICY(SET CMP0068 OLD)
-ENDIF()
-
 # If Carla was not provided by the system, make a dummy library instead
 if(LMMS_HAVE_WEAKCARLA)
   SET(CARLA_INCLUDE_DIRS