Ensured that the _GNU_SOURCE macro is defined in the prelude, as e.g. the pthread_rwlock_t type is hidden in <pthread.h> on Linux without it.
Ensured that the _GNU_SOURCE macro is defined in the prelude, as e.g. the
pthread_rwlock_t type is hidden in <pthread.h> on Linux without it.

dryproject/libcpr,dryproject/libcpr,dryproject/libcpr,dryproject/libcpr,dryproject/libcpr,dryproject/libcpr