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]
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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.