std.Build: do not override properties of a package like named modules

The `addModule` function could override the module that is visible to
dependants which most likely unintentional. Instead should asserts that
no existing module has been added with the given name.

The same issue applies to `addNamedWriteFiles` and `addNamedLazyPath`.

Author: Techatrix

lib/std/Build.zig

@@ -906,7 +906,13 @@ pub const AssemblyOptions = struct {
 /// `createModule` can be used instead to create a private module.
 pub fn addModule(b: *Build, name: []const u8, options: Module.CreateOptions) *Module {
     const module = Module.create(b, options);
-    b.modules.put(b.dupe(name), module) catch @panic("OOM");
+    const gop = b.modules.getOrPutValue(b.dupe(name), module) catch @panic("OOM");
+    if (gop.found_existing) {
+        panic(
+            "A module with the name '{s}' has already been added to the package. Consider creating a private module with std.Build.createModule",
+            .{name},
+        );
+    }
     return module;
 }
 
@@ -1025,12 +1031,24 @@ pub fn addWriteFile(b: *Build, file_path: []const u8, data: []const u8) *Step.Wr
 
 pub fn addNamedWriteFiles(b: *Build, name: []const u8) *Step.WriteFile {
     const wf = Step.WriteFile.create(b);
-    b.named_writefiles.put(b.dupe(name), wf) catch @panic("OOM");
+    const gop = b.named_writefiles.getOrPutValue(b.dupe(name), wf) catch @panic("OOM");
+    if (gop.found_existing) {
+        panic(
+            "A WriteFile step with the name '{s}' has already been added to the package. Consider creating a private WriteFile step with std.Build.addWriteFiles",
+            .{name},
+        );
+    }
     return wf;
 }
 
 pub fn addNamedLazyPath(b: *Build, name: []const u8, lp: LazyPath) void {
-    b.named_lazy_paths.put(b.dupe(name), lp.dupe(b)) catch @panic("OOM");
+    const gop = b.named_lazy_paths.getOrPutValue(b.dupe(name), lp) catch @panic("OOM");
+    if (gop.found_existing) {
+        panic(
+            "A LazyPath with the name '{s}' has already been added to the package.",
+            .{name},
+        );
+    }
 }
 
 pub fn addWriteFiles(b: *Build) *Step.WriteFile {