BUG: Fix a string comparison problem in ctkExecuteProcess.cmake.in

CMake/ctkExecuteProcess.cmake.in

@@ -30,15 +30,18 @@ EXECUTE_PROCESS(
   @CONFIG_ERROR_STRIP_TRAILING_WHITESPACE@
   )
 
-IF (NOT "@VARNAME_RESULT_VARIABLE@" STREQUAL "")
+SET(var "@VARNAME_RESULT_VARIABLE@")
+IF (NOT var STREQUAL "")
   SET(SETTER_RESULT_VARIABLE "SET(@VARNAME_RESULT_VARIABLE@ ${@VARNAME_RESULT_VARIABLE@} PARENT_SCOPE)")
 ENDIF()
 
-IF (NOT "@VARNAME_OUTPUT_VARIABLE@" STREQUAL "")
+SET(var "@VARNAME_OUTPUT_VARIABLE@")
+IF (NOT var STREQUAL "")
   SET(SETTER_OUTPUT_VARIABLE "SET(@VARNAME_OUTPUT_VARIABLE@ ${@VARNAME_OUTPUT_VARIABLE@} PARENT_SCOPE)")
 ENDIF()
 
-IF (NOT "@VARNAME_ERROR_VARIABLE@" STREQUAL "")
+SET(var "@VARNAME_ERROR_VARIABLE@")
+IF (NOT var STREQUAL "")
   SET(SETTER_ERROR_VARIABLE "SET(@VARNAME_ERROR_VARIABLE@ ${@VARNAME_ERROR_VARIABLE@} PARENT_SCOPE)")
 ENDIF()