Fix jack warnings

[pierreguillot]

This PR fixes an issue posted on the JUCE forum concerning -Wmissing-prototypes warnings due to JACK (tested with Clang 10.0.0 & Ubuntu 20.04 - Clang 14.0.0 & Ubuntu 22.04.5 but warnings should appear on other OS.).

[295/300] Building CXX object CMakeFiles/Partiels.dir/JUCE/modules/juce_audio_devices/juce_audio_devices.cpp.o
In file included from /home/runner/work/Partiels/Partiels/JUCE/modules/juce_audio_devices/juce_audio_devices.cpp:264:
/home/runner/work/Partiels/Partiels/JUCE/modules/juce_audio_devices/native/juce_JackAudio.cpp:72:42: warning: no previous prototype for function 'jack_client_open' [-Wmissing-prototypes]
JUCE_DECL_JACK_FUNCTION (jack_client_t*, jack_client_open, (const char* client_name, jack_options_t options, jack_status_t* status, ...), (client_name, options, status))
                                         ^
/home/runner/work/Partiels/Partiels/JUCE/modules/juce_audio_devices/native/juce_JackAudio.cpp:72:26: note: declare 'static' if the function is not intended to be used outside of this translation unit
JUCE_DECL_JACK_FUNCTION (jack_client_t*, jack_client_open, (const char* client_name, jack_options_t options, jack_status_t* status, ...), (client_name, options, status))
...

Github Action
job-logs.txt

The commit 784ff78 declares the JACK methods as static to avoid these warnings. Two methods are only used in Debug mode, so they generate the -Wunused-function warning in Release mode. The second commit c5eb15a corrects this problem by declaring them Debug-only.

[reuk]

Thanks, that's merged here: 08fcb74