[clang-tidy] Switch C headers to C++ ones

Found using modernize-return-braced-init-list

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/TLSClient.cpp

@@ -31,17 +31,13 @@
 #include <TLSClient.h>
 #include <iostream>
 #include <unistd.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <stdint.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstdint>
+#include <cstring>
 #include <sys/socket.h>
 #include <arpa/inet.h>
-#if (defined OPENBSD || defined SOLARIS || defined NETBSD)
-#include <errno.h>
-#else
-#include <sys/errno.h>
-#endif
+#include <cerrno>
 #include <sys/types.h>
 #include <netdb.h>
 #include <gnutls/x509.h>