When I am building my own image for my Mercury MAC1200R v2 (MT7628AN soc) using GCC 5.4 everything is working. I can flash the image just fine and it boots and runs (some errors still, different threads).
When I change from GCC 5.4 to 6.3 I get a kernel panic cause of missing init options. I didn't change anything else via make menuconfig.
Kernel panic - not syncing: No working init found. Try passing init= option to kernel. See Linux Documentation/init.txt for guidance.
Google reveals that this is usually a makefile "bug", but I fail to understand why the makefile would be different when changing compilers, so I am not sure where to start looking for the "bug".
Not sure if I need/should change to 6.3 anyway, but from what I understand the later version should optimize the code better (faster/smaller memory print)