'make check' fails after 'make debug'

Commit 31f27b672c05df602fa1cc9cb5f64f0ef7cb3d80 introduced a regression in the build. A make check fails after make debug:

misc.o:(.data+0x60): undefined reference to `__gcov_merge_add'
saveresume.o: In function `_GLOBAL__sub_I_65535_0_savefile':
/home/ninneman/devel/open-adventure/open-adventure/saveresume.c:127: undefined reference to `__gcov_init'
saveresume.o:(.data+0x60): undefined reference to `__gcov_merge_add'
collect2: error: ld returned 1 exit status
Makefile:47: recipe for target 'advent' failed
make: *** [advent] Error 1