[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`.
[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
Mark the `spin` variable in atomic.c as G_GNUC_UNUSED.

It would require an `#ifdef` forest to get the conditions
under which it is used right.
Bring the implementation of the 64-bit CAS fallback in line with the 32-bit one.