Windows compatibility fixes

VS2013 has trouble with relative include paths for apps/openssl, so move
certhash_win/apps_win.c back to apps/openssl.

gmtime_r on mingw64 fails with negative time_t, override

gmtime_s fails all of the time unit tests, override

SHUT_RD/WR are defined in newer mingw64 headers, check before overriding

apps/openssl/certhash_win.c

@@ -0,0 +1,13 @@
+/*
+ * Public domain
+ * certhash dummy implementation for platforms without symlinks
+ */
+
+#include <apps.h>
+
+int
+certhash_main(int argc, char **argv)
+{
+	fprintf(stderr, "certhash is not enabled on this platform\n");
+	return (1);
+}