build: fix circular header inclusion with other packages

This commit renames lib/setup.h to lib/curl_setup.h and
renames lib/setup_once.h to lib/curl_setup_once.h.

Removes the need and usage of a header inclusion guard foreign
to libcurl. [1]

Removes the need and presence of an alarming notice we carried
in old setup_once.h [2]

----------------------------------------

1 - lib/setup_once.h used __SETUP_ONCE_H macro as header inclusion guard
    up to commit ec691ca3 which changed this to HEADER_CURL_SETUP_ONCE_H,
    this single inclusion guard is enough to ensure that inclusion of
    lib/setup_once.h done from lib/setup.h is only done once.

    Additionally lib/setup.h has always used __SETUP_ONCE_H macro to
    protect inclusion of setup_once.h even after commit ec691ca3, this
    was to avoid a circular header inclusion triggered when building a
    c-ares enabled version with c-ares sources available which also has
    a setup_once.h header. Commit ec691ca3 exposes the real nature of
    __SETUP_ONCE_H usage in lib/setup.h, it is a header inclusion guard
    foreign to libcurl belonging to c-ares's setup_once.h

    The renaming this commit does, fixes the circular header inclusion,
    and as such removes the need and usage of a header inclusion guard
    foreign to libcurl. Macro __SETUP_ONCE_H no longer used in libcurl.

2 - Due to the circular interdependency of old lib/setup_once.h and the
    c-ares setup_once.h header, old file lib/setup_once.h has carried
    back from 2006 up to now days an alarming and prominent notice about
    the need of keeping libcurl's and c-ares's setup_once.h in sync.

    Given that this commit fixes the circular interdependency, the need
    and presence of mentioned notice is removed.

    All mentioned interdependencies come back from now old days when
    the c-ares project lived inside a curl subdirectory. This commit
    removes last traces of such fact.

1 files changed, 2 insertions, 2 deletions

diff --git a/tests/libtest/test.h b/tests/libtest/test.h
index fcc91ad8b..5de8c7c75 100644
--- a/tests/libtest/test.h
+++ b/tests/libtest/test.h
@@ -20,14 +20,14 @@
  *
  ***************************************************************************/
 
-/* Now include the setup.h file from libcurl's private libdir (the source
+/* Now include the curl_setup.h file from libcurl's private libdir (the source
    version, but that might include "curl_config.h" from the build dir so we
    need both of them in the include path), so that we get good in-depth
    knowledge about the system we're building this on */
 
 #define CURL_NO_OLDIES
 
-#include "setup.h"
+#include "curl_setup.h"
 
 #include <curl/curl.h>