Add -Wmissing-variable-declarations, with attendant fixes

This is a big-ish patch, but it's very straightforward.  Under this
clang warning, we're not actually allowed to have a global variable
without a previous extern declaration for it.  The cases where we
violated this rule fall into three roughly equal groups:
  * Stuff that should have been static.
  * Stuff that was global but where the extern was local to some
    other C file.
  * Stuff that was only global when built for the unit tests, that
    needed a conditional extern in the headers.

The first two were IMO genuine problems; the last is a wart of how
we build tests.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/test/test_socks.c b/src/test/test_socks.c
index 6da09fd653..62ff12fe15 100644
--- a/src/test/test_socks.c
+++ b/src/test/test_socks.c
@@ -34,7 +34,7 @@ socks_test_cleanup(const struct testcase_t *testcase, void *ptr)
   return 1;
 }
 
-const struct testcase_setup_t socks_setup = {
+static const struct testcase_setup_t socks_setup = {
   socks_test_setup, socks_test_cleanup
 };