atomic increment/decrement is provided by
osl_increment/decrementInterlockedCount()
but that is a exported dll function, so it cannot be inlined.

valgrind analysis of a run, loading a medium sized spreadsheet, shows
that these 2 functions were called 3.5 millions times for a total cost of
55 millions of instructions... a cost of 8 instructions per call,
which is at least a 300% overhead since an atomic inc/dec is 2 instructions
iow we could save about 1% of the total instruction count of that run(4.6B)

We cannot change the existing api, as this would break ABI.
but we can add a new api. and migrate internal user to it.

osl_atomic_decrement/osl_atomic_increment do the same task,
than osl_*IntelockedCount() but do that inlined if possible.

Note that this version only optimize the case GCC with atomic built-in.
but support for other case should not be very hard.

follows-up patches will replace the use of the osl_*InterlockedCount()
in the product with their osl_atomic_* equivalent.

Change-Id: If4dcbf94ea6f62eb6d55d30613fe65878ffb8023
Signed-off-by: Stephan Bergmann <sbergman@redhat.com>