Unless you want half your C logic to be error propagation, it’ll have to be <setjmp.h>, all its flaws notwithstanding. Manual unwinding can be done tastefully (see Tcl), but in the single-digit-KLOC weight class it’s not really a choice.

while we're marvelling about how small and compact it is, then just replace them (with something uglier and less performant), it's not rocket science