disable unit test by default on IOS build because compilation time has almost...

disable unit test by default on IOS build because compilation time has almost doubled since c++ code introduced

configs/config-ios.cmake

@@ -32,7 +32,7 @@ set(DEFAULT_VALUE_ENABLE_OPUS ON)
 set(DEFAULT_VALUE_ENABLE_SILK ON)
 set(DEFAULT_VALUE_ENABLE_SPEEX ON)
 set(DEFAULT_VALUE_ENABLE_SRTP ON)
-set(DEFAULT_VALUE_ENABLE_UNIT_TESTS ON)
+set(DEFAULT_VALUE_ENABLE_UNIT_TESTS OFF) #link of binary significantly slow down compilation.
 set(DEFAULT_VALUE_ENABLE_VCARD ON)
 set(DEFAULT_VALUE_ENABLE_VIDEO ON)
 set(DEFAULT_VALUE_ENABLE_VPX ON)