How do developers fix bugs when compiling takes so long?
Initial compiling of bitcoin-core can take a couple of minutes. If you have a multicore processor, you can use make -j&lt;cores+1&gt; to speed up compiling (parallel compiling).

Once bitcoin-core is compiled, a single semicolon change does (mostly) not require to recompile everything. You only compile the affected files (.cpp) again and do do the linking.

On most machines, compiling a simple change requires mostly less then 10 seconds.