[clang-repl] Improve flags responsible for generating shared wasm binaries (llvm#116735)

There are a couple changes in this PR that help getting clang-repl to
run in the browser. Using a jupyterlite instance for the example pasted
below

1) Updating flags responsible for generating shared wasm binaries that
need to be dynamically loaded Most Importantly as can be seen in the
changes `shared` and `allow-undefined` are crucial.

![image](https://github.com/user-attachments/assets/1183fd44-8951-496a-899a-e4af39a48447)

2) While exiting we encounter this.

![image](https://github.com/user-attachments/assets/9487a3f4-7200-471d-ba88-09e98ccbc47a)

Now as can be seen here

https://github.com/llvm/llvm-project/blob/cd418030de7ae75750bc4e48d1238baf03c675e5/clang/lib/Interpreter/Interpreter.cpp#L421-L430

We call cleanUP in the destructor. Now cleanUP through
IncrementalExecutor tries to deinitialize the JIT which wasn't even
intialized as runCtors in wasm.cpp is a no-op

https://github.com/llvm/llvm-project/blob/cd418030de7ae75750bc4e48d1238baf03c675e5/clang/lib/Interpreter/IncrementalExecutor.cpp#L94-L101

https://github.com/llvm/llvm-project/blob/cd418030de7ae75750bc4e48d1238baf03c675e5/clang/lib/Interpreter/Wasm.cpp#L107-L109
(cherry picked from commit 752dbd6)

Author: anutosh491

clang/lib/Interpreter/IncrementalExecutor.h

@@ -56,7 +56,7 @@ class IncrementalExecutor {
   virtual llvm::Error addModule(PartialTranslationUnit &PTU);
   virtual llvm::Error removeModule(PartialTranslationUnit &PTU);
   virtual llvm::Error runCtors() const;
-  llvm::Error cleanUp();
+  virtual llvm::Error cleanUp();
   llvm::Expected<llvm::orc::ExecutorAddr>
   getSymbolAddress(llvm::StringRef Name, SymbolNameKind NameKind) const;
 

clang/lib/Interpreter/Interpreter.cpp

@@ -192,7 +192,6 @@ IncrementalCompilerBuilder::CreateCpp() {
 #ifdef __EMSCRIPTEN__
   Argv.push_back("-target");
   Argv.push_back("wasm32-unknown-emscripten");
-  Argv.push_back("-pie");
   Argv.push_back("-shared");
 #endif
   Argv.insert(Argv.end(), UserArgs.begin(), UserArgs.end());

clang/lib/Interpreter/Wasm.cpp

@@ -72,13 +72,13 @@ llvm::Error WasmIncrementalExecutor::addModule(PartialTranslationUnit &PTU) {
   OutputFile.close();
 
   std::vector<const char *> LinkerArgs = {"wasm-ld",
-                                          "-pie",
+                                          "-shared",
                                           "--import-memory",
                                           "--no-entry",
                                           "--export-all",
                                           "--experimental-pic",
-                                          "--no-export-dynamic",
                                           "--stack-first",
+                                          "--allow-undefined",
                                           OutputFileName.c_str(),
                                           "-o",
                                           OutputFileName.c_str()};
@@ -109,6 +109,12 @@ llvm::Error WasmIncrementalExecutor::runCtors() const {
   return llvm::Error::success();
 }
 
+llvm::Error WasmIncrementalExecutor::cleanUp() const {
+  // Can't call cleanUp through IncrementalExecutor as it
+  // tries to deinitialize JIT which hasn't been initialized
+  return llvm::Error::success();
+}
+
 WasmIncrementalExecutor::~WasmIncrementalExecutor() = default;
 
 } // namespace clang

clang/lib/Interpreter/Wasm.h

@@ -28,6 +28,7 @@ class WasmIncrementalExecutor : public IncrementalExecutor {
   llvm::Error addModule(PartialTranslationUnit &PTU) override;
   llvm::Error removeModule(PartialTranslationUnit &PTU) override;
   llvm::Error runCtors() const override;
+  llvm::Error cleanUp() override;
 
   ~WasmIncrementalExecutor() override;
 };