Compilation: delete clang diag files afterwards

After parsing diagnostics files from clang we don't have any more use
for those tmp files. Delete them to reduce clutter and disk usage.

src/Compilation.zig

@@ -4530,6 +4530,9 @@ fn updateCObject(comp: *Compilation, c_object: *CObject, c_obj_prog_node: *std.P
                                 log.err("{}: failed to parse clang diagnostics: {s}", .{ err, stderr });
                                 return comp.failCObj(c_object, "clang exited with code {d}", .{code});
                             };
+                            zig_cache_tmp_dir.deleteFile(out_diag_path) catch |err| {
+                                log.warn("failed to delete '{s}': {s}", .{ out_diag_path, @errorName(err) });
+                            };
                             return comp.failCObjWithOwnedDiagBundle(c_object, bundle);
                         }
                     },