As explained by @AnnaBridge here: Several bugs in the Makefile (Online IDE export as makefile) - #4 by AnnaBridge
If it is the former [i.e. the Online Compiler] then it is unlikely to be looked at as the focus is on the replacement, Mbed Studio…
From my own experience when I stared with Mbed, the Makefile export was already not working well and quickly became a hell to work with…
I’m afraid (well actually no, I’m relived that they can focus on more important things, especially the new CMake tools), it’s not going to get fixed.
If you’re already fighting with the Makefile that doesn’t work, why waste your effort and not try something that does work? Be it Mbed Studio, USCRPL/mbed-cmake or the first party CMake support from Mbed?