Fix HAVE_PTHREAD_CONDATTR_SETCLOCK detection on Android

[MichalStrehovsky]

Android puts pthread stuff into libc. Because this wasn't detected, we are using some iOS fallbacks in System.Native. I'm propagating how pthreads are detected in the CoreCLR PAL (that was fixed up for Android in the CoreCLR PAL a couple years ago).

Failure to properly detect it here was causing build breaks in CoreCLR on Android (that's how I found this).

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[marek-safar]

@akoeplinger should we backport this?

[akoeplinger]

@akoeplinger should we backport this?

Ideally yes, though it's not completely without risk.

Note that we still have this definition in mono-os-mutex.h which disables use of pthread_condattr_setclock, presumably because there was some issue on earlier Android versions:

runtime/src/mono/mono/utils/mono-os-mutex.h

Lines 39 to 41 in 32df679

	#if !defined(CLOCK_MONOTONIC) || defined(HOST_DARWIN) || defined(HOST_ANDROID) || defined(HOST_WASM)
	#define BROKEN_CLOCK_SOURCE
	#endif

We might want to fix that as well. I also saw that we explicitly disable CLOCK_MONOTONIC for iOS since it was only available on iOS10+, but that is now our minimum target so we can likely remove that too.

[MichalStrehovsky]

Ideally yes, though it's not completely without risk.

I filed #58737 and put it into 6.0 milestone. FWIW, the old commit that disabled it on Mono on Android just talks about fixing a build break and doesn't have much else to go off.

[ViktorHofer]

@MichalStrehovsky I think this change is causing the CoreCLR GCC Product Build Linux x64 leg to fail in all PRs: #58744.