Link Android's log with PRIVATE visibility (#2815)

INTERFACE should be used on dependencies from other than our source files.
PRIVATE should be used the include happens in our source files.

In this case (src/catch2/internal/catch_debug_console.cpp:20) the include
is from our source file.

I encountered a issue with this when building Catch2 for Android in
combination with BUILD_SHARED_LIBS. Changing the visibility to PRIVATE
fixes the issue.

src/CMakeLists.txt

@@ -354,7 +354,7 @@ endif()
 add_library(Catch2::Catch2 ALIAS Catch2)
 
 if (ANDROID)
-    target_link_libraries(Catch2 INTERFACE log)
+    target_link_libraries(Catch2 PRIVATE log)
 endif()
 
 set_target_properties(Catch2 PROPERTIES