- dnl we need to define _XOPEN_SOURCE=500 to get PTHREAD_MUTEX_RECURSIVE
- dnl with glibc 2.1+, it probably shouldn't hurt elsewhere?
+ dnl we need _GNU_SOURCE to get PTHREAD_MUTEX_RECURSIVE with glibc 2.1+
+ dnl (strictly speaking we only need _XOPEN_SOURCE=500 but just defining
+ dnl this disables _BSD_SOURCE which breaks libtiff compilation, so it is
+ dnl simpler to just define _GNU_SOURCE to get everything)