Cygwin doesn't have SI_TKILL, fine.

c++/src/kj/async-unix-test.c++

@@ -117,7 +117,9 @@ TEST_F(AsyncUnixTest, SignalsAsync) {
       [&](siginfo_t&& info) {
     received = true;
     EXPECT_EQ(SIGUSR2, info.si_signo);
+#if __linux__
     EXPECT_SI_CODE(SI_TKILL, info.si_code);
+#endif
   });
 
   delay();

mega-test-quick.cfg

 linux-gcc-4.7      1632 ./super-test.sh tmpdir capnp-gcc-4.7 quick
 linux-gcc-4.8      1635 ./super-test.sh tmpdir capnp-gcc-4.8 quick gcc-4.8
 linux-clang        1652 ./super-test.sh tmpdir capnp-clang quick clang
-mac                 758 ./super-test.sh remote beat caffeinate quick
+mac                 765 ./super-test.sh remote beat caffeinate quick
 cygwin              769 ./super-test.sh remote Kenton@flashman quick