build: assert wlroots version at comptime

This will prevent people compiling river against the wrong wlroots
version and wondering why it crashes.

 deps/zig-wlroots | 2 +-
 river/main.zig   | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/deps/zig-wlroots b/deps/zig-wlroots
index c5f7594..b270171 160000
--- a/deps/zig-wlroots
+++ b/deps/zig-wlroots
@@ -1 +1 @@
-Subproject commit c5f759484ec2bb6afdee54053f5b0aaccf060131
+Subproject commit b270171f7bfe19eb15c1bb2b20121dd9e7ac32f7
diff --git a/river/main.zig b/river/main.zig
index 874b518..3a2d5ee 100644
--- a/river/main.zig
+++ b/river/main.zig
@@ -16,9 +16,17 @@
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
 const std = @import("std");
+const assert = std.debug.assert;
 const os = std.os;
+
 const wlr = @import("wlroots");
 
+// River requires wlroots 0.14
+comptime {
+    assert(wlr.version.major == 0);
+    assert(wlr.version.minor == 14);
+}
+
 const build_options = @import("build_options");
 
 const c = @import("c.zig");