GHC API displays linker messages to stdout instead of via log_action
At least in the LinkInMemory mode, GHC API displays linker messages, such as
Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done.
on stdout instead of using the log_action handler for them, just as for all the other kinds of messages. Moreover, I haven't found any way of suppressing these messages apart of setting verbosity=0, which turns off other important messages. I can see no GHC flags that does this and this linker does not accept any special linker flags. I don't know the policy about severity levels, but I suppose severity SevOutput could be fine for these messages, by similarity to "compiling M ... done." messages which have such severity.