xplat: ICU fallback only if custom path wasn't provided

CMakeLists.txt

@@ -194,7 +194,9 @@ elseif(CC_TARGET_OS_OSX)
         -DPLATFORM_UNIX
     )
 
-    if(NOT ICULIB)
+    # in case ICU path was given but it doesn't exist, build script will fail.
+    # so, fallback only if ICU path wasn't given
+    if(NOT ICU_INCLUDE_PATH)
       set(NO_ICU_PATH_GIVEN 1)
       message("-- Couldn't find ICU. Falling back to --no-icu build")
     endif()