On systems where gnutls uses libgcrypt, I'm seeing the following
build failure
libvirt.c:314: error: variable 'virTLSThreadImpl' has initializer but incomplete type
libvirt.c:319: error: 'GCRY_THREAD_OPTION_PTHREAD' undeclared here (not in a function)
...
Fix by undefining WITH_GNUTLS_GCRYPT in config-post.h
# undef WITH_CURL
# undef WITH_DTRACE_PROBES
# undef WITH_GNUTLS
+# undef WITH_GNUTLS_GCRYPT
# undef WITH_MACVTAP
# undef WITH_NUMACTL
# undef WITH_SASL