More improvements for macOS and conky generally

[npyl]

Hi!
This is some work on both general stuff and macOS specific stuff. 😝

General Changes

• Activated the option BUILD_WLAN for all OSs (set to false by default)
• Fixed $wireless_essid (also affected Linux, probably other OS, too!) crashing conky when no arg was passed. Correct behaviour would be to allocate dev with default interface (e.g. eth0). Adding parse_net_stat_arg fixes the problem.
• Removed interface name from $downspeed and $upspeed from conky.conf and conky_no_x11.conf; we want conky to always use the DEFAULTNETDEV which is set during configuration with cmake and my vary from OS to OS. This is part of 147499f.

macOS Changes

• Fixed $if_up by removing the SOCK_CLOEXEC flag from socket() in net_stats.cc when building for macOS; for some reason the function fails with error 43: Protocol not supported. This may also affect linux but I haven't checked yet.
• Improve support for macOS (Patches for #29 and #26 are applied automatically now as of 147499f during cmake configuration)
• Improve get_freq() using the Intel Power Gadget API if BUILD_IPGFREQ is enabled.
• Add build option BUILD_IPGFREQ (set to false by default) so that the user can choose whether to use IPG or stick with old behaviour (Print constant factory frequency of CPU).

IPG (Intel Power Gadget concerns)

Intel Power Gadget can be installed using Homebrew-cask and it installs a .app, a Framework and a kernel-extension. This will seem a bit troublesome in my opinion for many users thus the BUILD_IPGFREQ option.
Now, one has the option to either use a better $freq or avoid the hussle of installing a library/kernel extension (with sacrifices).

NOTE: IPG doesn't seem to support multiple cores although stating the opposite in the documentation thus, all readings are for core0.

More Concerns

I am not sure if using Objective-C++ in darwin.mm will be a problem for sonar but if there is a problem I will work it out.

Epilogue

This is a prequel; actual support for WLAN on macOS is coming soon!

[brndnmtthws]

Let me make you a collaborator, and you can push your branch directly to this repo.

[npyl]

There must be some problem with sonar, probably because I changed darwin.cc to darwin.mm for Objective-C++, I will have to investigate this.

[brndnmtthws]

@npyl Sonar doesn't work with external pull requests. The PR must originate from a branch on this repo, so it won't pass with this PR.

[brndnmtthws]

@npyl Have a look at #579, the sonar checks should run on that PR.

[npyl]

I see!! Thats great! But still, why hasn't it passed the check yet? Sonar has been going from the moment I opened the PR

[brndnmtthws]

@npyl it can take 5-10 minutes.