fix var defs for catch vars (closes #4757)

analyzer.ml

@@ -1267,6 +1267,7 @@ module TexprTransformer = struct
 						declare_var ctx.graph v;
 						let scope = increase_scope() in
 						let bb_catch = create_node BKNormal bb_exc e.etype e.epos in
+						add_var_def g bb_catch v;
 						add_cfg_edge g bb_exc bb_catch CFGGoto;
 						let bb_catch_next = block bb_catch e in
 						scope();

tests/unit/src/unit/issues/Issue4757.hx

@@ -6,6 +6,22 @@ class Issue4757 extends Test {
 		eq('ca: 2, cb: 1', cunion(1, 2));
 	}
 
+	function test2() {
+		var cb = getInt();
+		var result = "";
+		try {
+			throw 1;
+		} catch (ca:Int) {
+			var tmp = ca;
+			ca = cb;
+			cb = tmp;
+			result = 'ca: $ca, cb: $cb';
+		}
+		eq('ca: 2, cb: 1', result);
+	}
+
+	static function getInt() return 2;
+
 	static function cunion(ca:Int, cb:Int) {
 		var tmp = ca;
 		ca = cb;