darwin: Building with CGO produces warning

[bwplotka]

# github.com/prometheus/client_golang/prometheus
In file included from process_collector_cgo_darwin.c:21:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/mach/shared_memory_server.h:48:2: warning: "<mach/shared_memory_server.h> is deprecated.  Please use <mach/shared_region.h> instead." [-W#warnings]

This is on the latest client_golang (main) version, likely after https://github.com/prometheus/client_golang/pull/1616

Does not look serious, but something to fix cc @mharbison72