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 #1616

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

[bwplotka]

This is a bit annoying because everyone who develops on Mac on binaries that import client_golang have this warning (by default e.g. on Goland CGO is enabled) 🤔 e.g. when running tests.

[mharbison72]

Unfortunately, they don't provide a replacement header with a couple of constants that are used, and I'm not aware of any #pragma style directives that can be put into the code to suppress a #warning. The Apple repos have now been updated with the new OS release from last month, and nothing has changed in this area. That leaves us with a couple of hacky options:

1. Copy the constants from the header, and don't include the header itself
2. See if there's some CFLAGS option to suppress #warning directives
3. Drop the adjustment of the value that's being done

The first is probably the easiest, and probably my preference (and add a #warning if the architecture isn't supported, since the constants are arch specific?).

The second seems too broad.

The third is a possibility, because as mentioned in the commit comment and the code, I've never seen the adjustment amount be non-zero. But if there's a case that could happen, we wouldn't report the same value as ps(1).

What do you think?