aarch64: use compiler flag outline-atomics if available

outline-atomics compilation flag changes behaviour of builtin_atomics,
by adding runtime detection of LSE atomics. If these are supported, they
will be used. This gains LSE atomics use without hurting compatibility
with older aarch64 machines.

configure.cmake

@@ -69,6 +69,11 @@ IF(CMAKE_SYSTEM_PROCESSOR STREQUAL "i686" AND CMAKE_COMPILER_IS_GNUCC AND
   SET(PLUGIN_QUERY_RESPONSE_TIME NO CACHE BOOL "Disabled, gcc is too old")
 ENDIF()
 
+# use runtime atomic-support detection in aarch64
+IF(CMAKE_SYSTEM_PROCESSOR MATCHES "aarch64")
+  MY_CHECK_AND_SET_COMPILER_FLAG("-moutline-atomics")
+ENDIF()
+
 IF(WITHOUT_DYNAMIC_PLUGINS)
   MESSAGE("Dynamic plugins are disabled.")
 ENDIF(WITHOUT_DYNAMIC_PLUGINS)