+** make maintainer-check-valgrind
+This target uses valgrind both to check bison, and the generated parsers.
+
+This is not mature on Mac OS X. First, Valgrind does support the way bison
+calls m4, so Valgrind cannot be used to check bison on Mac OS X.
+
+Second, there are many errors that come from the platform itself, not from
+bison. build-aux/darwin11.4.0.valgrind addresses some of them.
+
+Third, valgrind issues warnings such as:
+
+ --99312:0:syswrap- WARNING: Ignoring sigreturn( ..., UC_RESET_ALT_STACK );
+
+which cause the test to fail uselessly. It is hard to ignore these errors
+with a major overhaul of the way instrumentation is performed in the test
+suite. So currently, do not try to run valgrind on Mac OS X.
+