Uncoditionally include errno.h instead of guessing

POSIX tells us that it is errno.h, musl fails to build with -Werror
because it redirects sys/errno.h->errno.h and uses #warning

(cherry picked from commit 041248e7cc)

src/TLSClient.cpp

@@ -37,11 +37,7 @@
 #include <string.h>
 #include <sys/socket.h>
 #include <arpa/inet.h>
-#if (defined OPENBSD || defined SOLARIS || defined NETBSD || defined HAIKU)
 #include <errno.h>
-#else
-#include <sys/errno.h>
-#endif
 #include <sys/types.h>
 #include <netdb.h>
 #include <gnutls/x509.h>