[Mono.Parallel] Removed broken Mono.Threading.Tasks code

The code in MonoTaskExtensions.cs relied on the internal method Execute(Action<Task>) in System.Threading.Tasks.Task which was removed in 0a66e60.
Added stress test to ConcurrentQueue.TryPeek.
The test checks that in some race condition the queue does not return null.
Changed TryPeek to handle race condition with Dequeue.
Dequeue sets the head.Value to its default. When TryPeek is interrupted in the process of retrieving the value some times Dequeue sets the value to its default. TryPeek now checks the head has not been changed before returning the value.
Fix formatting specifiers for some size_t arguments.
Add suggested parentheses to RHS of ^ operator.
Fix a bunch of warnings caused by unused functions.
Silence a bunch of unused result warnings in proflog.c.
Fix volatile pointer casts in proflog.c.
Silence some warnings in decode.c.
Fix a ton of printf formatting warnings in decode.c.
Use G_GNUC_UNUSED instead of commenting out variable declarations.

The previous approach resulted in mixed decls/stmts warnings.
Fix printf formatting warnings in mono-counters.c.
[counters] Add counters documentation to man page
Remove a #warning in security.c which gets triggered on OS X.
Fix a warning in atomic.c.
Disable `perf` support in the profiler when running on Android (for now).

We need to assess the situation before we enable this everywhere. Apparently
some older devices have trouble with `perf`.
[x86] Arguments to calls are passed via moves, instead of pushes.

I release these changes under the MIT license.
[arm] Fix OP_ATOMIC_CAS_I4.
Revert "Fix a warning in atomic.c."

This reverts commit 1fdc8789a7f4bfc6fa7f67c126569765194a3b6c.

This breaks the ios build:

../../../../../mono/mono/utils/atomic.c: In function ‘InterlockedCompareExchange64’:
../../../../../mono/mono/utils/atomic.c:572: error: ‘spin’ undeclared (first use in this function)
../../../../../mono/mono/utils/atomic.c:572: error: (Each undeclared identifier is reported only once
../../../../../mono/mono/utils/atomic.c:572: error: for each function it appears in.)
Merge branch 'master' of github.com:mono/mono