[OSX] Fix namespacing bug in cmath functions

This commit fixes the below errors on OSX compilers:
error: use of undeclared identifier 'isinf'
error: use of undeclared identifier 'isnan'; did you mean 'std::isnan'?
[OSX] Fix build for gutil in OSX

Fixes the below errors (we include x86 headers cause OSX is on Intel
now, and we declare a function not otherwise found on OSX)::
fatal error: 'gutil/atomicops-internals-macosx.h' file not found
error: use of undeclared identifier 'CLOCK_REALTIME'
[OSX] Explicitly declare clock_gettime on OSX
[OSX] Fix use of std::max(...) in OSX

The use of int64_t evaluates in stdc++ as 'long long' instead of long,
causing the std:max(...) to fail with mismatched argument errors, as
below:

error: no matching function for call to 'max'
note: candidate template ignored: deduced conflicting types for
parameter '_Tp' ('long' vs. 'long long')
[OSX] Make getrusage call pass on OSX

This fix is un-tested really, and simply declares a Linux-only constant
of RUSAGE_THREAD. This is likely not going to work when called, probably
ending up in a segfault or bad results, but at this point we're just
trying to make the build work so it can be revisited to be reimplemented
to use OSX's MACH libraries instead.
[OSX] Undefine PAGE_SIZE in hash-table.cc

This is done to avoid it being mapped to literal '4096' from MACH
includes on OSX. The below error was seen:

/Users/harshchouraria/Work/code/cloudera/impala/be/src/exec/hash-table.cc:36:18:
error: expected unqualified-id
static const int PAGE_SIZE = 8 * 1024 * 1024;
from macro 'PAGE_SIZE'
from macro 'I386_PGBYTES'
evaluating to 4096.
[OSX] Fix more min/max call mismatch oddities

Similar to previous commit, fixes literals to use LL instead of L so
they match with the evaluation of int64_t on OSX platforms.