make `@trap` return unreachable/noreturn (#15749)

`@trap` is a special function that we know never returns so it should
behave just like `@panic` and `@compileError` do currently and cause the
"unreachable code" + "control flow is diverted here" compile error.
Currently, `@trap(); @trap();` does not cause this error. Now it does.

1 files changed, 23 insertions, 0 deletions

diff --git a/test/cases/compile_errors/noreturn_builtins_divert_control_flow.zig b/test/cases/compile_errors/noreturn_builtins_divert_control_flow.zig
new file mode 100644
index 0000000000..32627f1652
--- /dev/null
+++ b/test/cases/compile_errors/noreturn_builtins_divert_control_flow.zig
@@ -0,0 +1,23 @@
+export fn entry1() void {
+    @trap();
+    @trap();
+}
+export fn entry2() void {
+    @panic("");
+    @panic("");
+}
+export fn entry3() void {
+    @compileError("");
+    @compileError("");
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:5: error: unreachable code
+// :2:5: note: control flow is diverted here
+// :7:5: error: unreachable code
+// :6:5: note: control flow is diverted here
+// :11:5: error: unreachable code
+// :10:5: note: control flow is diverted here