ver 3.4 allow override CPM location (#6)

Author: Arniiiii

cmake/getCPM.cmake

@@ -35,19 +35,27 @@
 # set(CPM_DOWNLOAD_VERSION 0.40.2) set(CPM_HASH_SUM
 # "c8cdc32c03816538ce22781ed72964dc864b2a34a310d3b7104812a5ca2d835d")
 
-if(CPM_SOURCE_CACHE)
-  set(CPM_DOWNLOAD_LOCATION "${CPM_SOURCE_CACHE}/cpm/CPM_${CPM_DOWNLOAD_VERSION}.cmake")
-elseif(DEFINED ENV{CPM_SOURCE_CACHE})
-  set(CPM_DOWNLOAD_LOCATION "$ENV{CPM_SOURCE_CACHE}/cpm/CPM_${CPM_DOWNLOAD_VERSION}.cmake")
-else()
-  set(CPM_DOWNLOAD_LOCATION "${CMAKE_BINARY_DIR}/cmake/CPM_${CPM_DOWNLOAD_VERSION}.cmake")
+if(NOT DEFINED CPM_DOWNLOAD_LOCATION AND NOT DEFINED ENV{CPM_DOWNLOAD_LOCATION})
+  if(CPM_SOURCE_CACHE)
+    set(CPM_DOWNLOAD_LOCATION
+        "${CPM_SOURCE_CACHE}/cpm/CPM_${CPM_DOWNLOAD_VERSION}.cmake")
+  elseif(DEFINED ENV{CPM_SOURCE_CACHE})
+    set(CPM_DOWNLOAD_LOCATION
+        "$ENV{CPM_SOURCE_CACHE}/cpm/CPM_${CPM_DOWNLOAD_VERSION}.cmake")
+  else()
+    set(CPM_DOWNLOAD_LOCATION
+        "${CMAKE_BINARY_DIR}/cmake/CPM_${CPM_DOWNLOAD_VERSION}.cmake")
+  endif()
+
+  # Expand relative path. This is important if the provided path contains a
+  # tilde (~)
+  get_filename_component(CPM_DOWNLOAD_LOCATION ${CPM_DOWNLOAD_LOCATION}
+                         ABSOLUTE)
+
+  file(DOWNLOAD
+       https://raw.githubusercontent.com/Arniiiii/CPM.cmake/main/cmake/CPM.cmake
+       ${CPM_DOWNLOAD_LOCATION} # EXPECTED_HASH SHA256=${CPM_HASH_SUM}
+  )
 endif()
 
-# Expand relative path. This is important if the provided path contains a tilde (~)
-get_filename_component(CPM_DOWNLOAD_LOCATION ${CPM_DOWNLOAD_LOCATION} ABSOLUTE)
-
-file(DOWNLOAD https://raw.githubusercontent.com/Arniiiii/CPM.cmake/main/cmake/CPM.cmake
-     ${CPM_DOWNLOAD_LOCATION} # EXPECTED_HASH SHA256=${CPM_HASH_SUM}
-)
-
 include(${CPM_DOWNLOAD_LOCATION})