Including C headers inside of extern "C" breaks use from C++. Hoist
the includes of standard C headers above the block so we don't try
to mangle the stdlib.

See https://gitlab.freedesktop.org/pipewire/pipewire/-/merge_requests/2377 in
PipeWire where they bundle some JACK headers, so came across this.

Found via `codespell -q 3`

git-svn-id: http://subversion.jackaudio.org/jack/jack2/trunk/jackmp@3231 0c269be4-1314-0410-8aa9-9f06e86f4224

git-svn-id: http://subversion.jackaudio.org/jack/jack2/trunk/jackmp@1619 0c269be4-1314-0410-8aa9-9f06e86f4224

git-svn-id: http://subversion.jackaudio.org/jack/jack2/trunk/jackmp@1614 0c269be4-1314-0410-8aa9-9f06e86f4224

git-svn-id: http://subversion.jackaudio.org/jack/jack2/trunk/jackmp@1210 0c269be4-1314-0410-8aa9-9f06e86f4224

git-svn-id: http://subversion.jackaudio.org/jack/jack2/trunk/jackmp@1195 0c269be4-1314-0410-8aa9-9f06e86f4224