20865: Don't use getentropy() on OSX Sierra.

Tor 0.2.9 has a broader range of fixes and workarounds here, but for
0.2.8, we're just going to maintain the existing behavior.

(The alternative would be to backport both
1eba088054 and
16fcbd21c9 , but the latter is kind of
a subtle kludge in the configure.ac script, and I'm not a fan of
backporting that kind of thing.)

src/common/crypto.c

@@ -88,6 +88,15 @@
 
 #include "keccak-tiny/keccak-tiny.h"
 
+#ifdef __APPLE__
+/* Apple messed up their getentropy definitions in Sierra.  It's not insecure
+ * or anything (as far as I know) but it makes compatible builds hard.  0.2.9
+ * contains the necessary tricks to do it right: in 0.2.8, we're just using
+ * this blunt instrument.
+ */
+#undef HAVE_GETENTROPY
+#endif
+
 #ifdef ANDROID
 /* Android's OpenSSL seems to have removed all of its Engine support. */
 #define DISABLE_ENGINES