patch 8.1.1541: check for ASAN is not reliable

Problem:    Check for ASAN is not reliable.
Solution:   Check the version output. (Dominique Pelle, closes #4543)

src/testdir/test_memory_usage.vim

@@ -6,7 +6,7 @@ endif
 if has('gui_running')
   throw 'Skipped, does not work in GUI'
 endif
-if $ASAN_OPTIONS !=# ''
+if execute('version') =~# '-fsanitize=[a-z,]*\<address\>'
   " Skip tests on Travis CI ASAN build because it's difficult to estimate
   " memory usage.
   throw 'Skipped, does not work with ASAN'