darwin/Platform.c: do not include non-existing headers which break build

[barracuda156]

Commit ed7eac5 unconditionally includes a header which is not present on earlier macOS. This unnecessarily breaks the build. Use includes correctly.

[barracuda156]

Everything looks good now:

[barracuda156]

@BenBE Thank you, I have dropped AvailabilityMacros header from Platform.h now, the fallback now is in Platform.c.

(Perhaps there is little point to make a specific check here, we know that prior to 10.9 there is no folder for types in /usr/include/sys, SDKs are public, and the files are specifically for Darwin, no surprises here.)

[Explorer09]

@barracuda156 htop coding style prefers not to have a version number check in order to determine whether a header is available. You may mention the version number in code comments, but we would like the header availability be checked in configure.ac instead.

[barracuda156]

@Explorer09 Ok, let me make recommended changes, confirm that such solution will actually work and then rebase the PR.

[barracuda156]

@Explorer09 Could you please review?

[barracuda156]

@Explorer09 @BenBE I have switched to a simpler version which just replaces the included header with the universally supported one, as suggested by @ryandesign above.