CTestTest2: Avoid running purify unless requested

Tests/CTestTest2/test.cmake.in

@@ -15,13 +15,12 @@ SET(CTEST_MEMORYCHECK_SUPPRESSIONS_FILE "@MEMORYCHECK_SUPPRESSIONS_FILE@")
 SET(CTEST_MEMORYCHECK_COMMAND_OPTIONS   "@MEMORYCHECK_COMMAND_OPTIONS@")
 SET(CTEST_COVERAGE_COMMAND              "@COVERAGE_COMMAND@")
 SET(CTEST_NOTES_FILES                   "${CTEST_SCRIPT_DIRECTORY}/${CTEST_SCRIPT_NAME}")
-# for unix purify has to be used as a linker, and
-# will not work with ctest.  So disable it so
-# that it is not attempted.
-IF(UNIX)
-  IF("${CTEST_MEMORYCHECK_COMMAND}" MATCHES purify)
-    SET(CTEST_MEMORYCHECK_COMMAND)
-  ENDIF()
+
+# By default, CTESTTEST2_USE_PURIFY is not defined. If you want to run purify
+# on CTestTest2, set CTESTTEST2_USE_PURIFY to ON in CMake's cache.
+SET(CTESTTEST2_USE_PURIFY @CTESTTEST2_USE_PURIFY@)
+IF("${CTEST_MEMORYCHECK_COMMAND}" MATCHES purify AND NOT CTESTTEST2_USE_PURIFY)
+  SET(CTEST_MEMORYCHECK_COMMAND)
 ENDIF()
 
 #CTEST_EMPTY_BINARY_DIRECTORY(${CTEST_BINARY_DIRECTORY})