configure: Add --enable-compiler-atomic-builtins option

If the toolchain supports atomic builtins and the user ask for atomic
builtins, use them for the uatomic API. This requires that the
toolchains used to compile the library and the user application supports
such builtins.

The advantage of using these builtins is that they are well known
synchronization primitives by several tools such as TSAN.

However, they may introduce redundant memory barriers, mainly on
strongly ordered architectures.

Change-Id: Ia8e97112681f744f17816dbc4cbbec805a483331
Co-authored-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Olivier Dion <odion@efficios.com>
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>