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, 1 insertions, 1 deletions

diff --git a/include/curl/curlrules.h b/include/curl/curlrules.h
index 4e9c88003..7c2ede35b 100644
--- a/include/curl/curlrules.h
+++ b/include/curl/curlrules.h
@@ -190,7 +190,7 @@ typedef char
  * CURL_ISOCPP and CURL_OFF_T_C definitions are done here in order to allow
  * these to be visible and exported by the external libcurl interface API,
  * while also making them visible to the library internals, simply including
- * setup.h, without actually needing to include curl.h internally.
+ * curl_setup.h, without actually needing to include curl.h internally.
  * If some day this section would grow big enough, all this should be moved
  * to its own header file.
  */