gnutls: Use libgnurx instead of libpcreposix

It's more widely used and has fewer dependencies.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
geos: Enable shared builds

Modifications: don't define GEOS_INLINE.

See #534.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
libgeotiff: Enable shared

Signed-off-by: Timothy Gu <timothygu99@gmail.com>