I wish I had a simpler way of tracking these buggers down.
Created attachment 605595 [details] [diff] [review] Fix a bunch of "inlined function used but not defined" warnings
One trick is to change the signature of the inline function's declaration, and compile the file giving those warnings. gdb at least should then give a not-useless error message pointing to the call it found.
Ooh, that sounds much nicer than what I was doing! I would compile without -j to see what .cpp generated the warning, then delete everything in that file but the #includes, then binary search through those (expanding them inline into the file when I found one, and recursing). And even then it was sometimes totally cryptic why a particular header would trigger the warnings.