Fix build: linenoise needs to specify/propagate its include dir.

Change-Id: I1433aa6c357feaf8a51a9afe37412d74f37933a6
diff --git a/BUILD.gn b/BUILD.gn
index d6e7906..240b978 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -25,7 +25,13 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+config("linenoise_config") {
+  include_dirs = [ "." ]
+}
+
 static_library("linenoise") {
+  public_configs = [ ":linenoise_config" ]
+
   sources = [
     "linenoise.c",
     "linenoise.h",