Restore policy changes in CPMAddPackage (#388)

* Restore policy changes in CPMAddPackage

Fixes #387

* Correct style issues found by CI

Author: robertmaynard

cmake/CPM.cmake

@@ -67,22 +67,25 @@ endif()
 
 set_property(GLOBAL PROPERTY CPM_INITIALIZED true)
 
-# the policy allows us to change options without caching
-cmake_policy(SET CMP0077 NEW)
-set(CMAKE_POLICY_DEFAULT_CMP0077 NEW)
-
-# the policy allows us to change set(CACHE) without caching
-if(POLICY CMP0126)
-  cmake_policy(SET CMP0126 NEW)
-  set(CMAKE_POLICY_DEFAULT_CMP0126 NEW)
-endif()
+macro(cpm_set_policies)
+  # the policy allows us to change options without caching
+  cmake_policy(SET CMP0077 NEW)
+  set(CMAKE_POLICY_DEFAULT_CMP0077 NEW)
+
+  # the policy allows us to change set(CACHE) without caching
+  if(POLICY CMP0126)
+    cmake_policy(SET CMP0126 NEW)
+    set(CMAKE_POLICY_DEFAULT_CMP0126 NEW)
+  endif()
 
-# The policy uses the download time for timestamp, instead of the timestamp in the archive. This
-# allows for proper rebuilds when a projects url changes
-if(POLICY CMP0135)
-  cmake_policy(SET CMP0135 NEW)
-  set(CMAKE_POLICY_DEFAULT_CMP0135 NEW)
-endif()
+  # The policy uses the download time for timestamp, instead of the timestamp in the archive. This
+  # allows for proper rebuilds when a projects url changes
+  if(POLICY CMP0135)
+    cmake_policy(SET CMP0135 NEW)
+    set(CMAKE_POLICY_DEFAULT_CMP0135 NEW)
+  endif()
+endmacro()
+cpm_set_policies()
 
 option(CPM_USE_LOCAL_PACKAGES "Always try to use `find_package` to get dependencies"
        $ENV{CPM_USE_LOCAL_PACKAGES}
@@ -494,6 +497,7 @@ endfunction()
 
 # Download and add a package from source
 function(CPMAddPackage)
+  cpm_set_policies()
 
   list(LENGTH ARGN argnLength)
   if(argnLength EQUAL 1)