ExternalProject: Strip trailing space from git hash

Modules/ExternalProject.cmake

@@ -454,6 +454,7 @@ execute_process(
   WORKING_DIRECTORY \"${work_dir}\"
   RESULT_VARIABLE error_code
   OUTPUT_VARIABLE head_sha
+  OUTPUT_STRIP_TRAILING_WHITESPACE
   )
 if(error_code)
   message(FATAL_ERROR \"Failed to get the hash for HEAD\")
@@ -479,6 +480,7 @@ execute_process(
   WORKING_DIRECTORY \"${work_dir}\"
   RESULT_VARIABLE error_code
   OUTPUT_VARIABLE tag_sha
+  OUTPUT_STRIP_TRAILING_WHITESPACE
   )
 
 # Is the hash checkout out that we want?