add test case for previous commit

closes #2467

test/compile_errors.zig

@@ -2,6 +2,16 @@ const tests = @import("tests.zig");
 const builtin = @import("builtin");
 
 pub fn addCases(cases: *tests.CompileErrorContext) void {
+    cases.add(
+        "peer cast then implicit cast const pointer to mutable C pointer",
+        \\export fn func() void {
+        \\    var strValue: [*c]u8 = undefined;
+        \\    strValue = strValue orelse c"";
+        \\}
+    ,
+        "tmp.zig:3:32: error: cast discards const qualifier",
+    );
+
     cases.add(
         "attempt to cast enum literal to error",
         \\export fn entry() void {