[lld][WebAssembly] Improve error message on adding LTO object post-LTO. NFC (#66688)

We have been getting errors from emscripten users where including the
name of the symbol that triggered the inclusion would be useful in the
diagnosis. e.g:
https://github.com/emscripten-core/emscripten/issues/20275

lld/test/wasm/lto/libcall-truncsfhf2.ll

diff --git a/lld/test/wasm/lto/libcall-truncsfhf2.ll b/lld/test/wasm/lto/libcall-truncsfhf2.ll
index 1eea2b2..08b334a 100644
--- a/lld/test/wasm/lto/libcall-truncsfhf2.ll
+++ b/lld/test/wasm/lto/libcall-truncsfhf2.ll
@@ -17,4 +17,4 @@
   ret void
 }
 
-; CHECK: wasm-ld: error: {{.*}}truncsfhf2.o): attempt to add bitcode file after LTO.
+; CHECK: wasm-ld: error: {{.*}}truncsfhf2.o): attempt to add bitcode file after LTO (__truncsfhf2)

lld/wasm/InputFiles.cpp

diff --git a/lld/wasm/InputFiles.cpp b/lld/wasm/InputFiles.cpp
index fa20a35..96ac1e1 100644
--- a/lld/wasm/InputFiles.cpp
+++ b/lld/wasm/InputFiles.cpp
@@ -760,7 +760,7 @@
                 sym->getName());
 
   InputFile *obj = createObjectFile(mb, getName(), c.getChildOffset());
-  symtab->addFile(obj);
+  symtab->addFile(obj, sym->getName());
 }
 
 static uint8_t mapVisibility(GlobalValue::VisibilityTypes gvVisibility) {
@@ -826,9 +826,9 @@
 
 bool BitcodeFile::doneLTO = false;
 
-void BitcodeFile::parse() {
+void BitcodeFile::parse(StringRef symName) {
   if (doneLTO) {
-    error(toString(this) + ": attempt to add bitcode file after LTO.");
+    error(toString(this) + ": attempt to add bitcode file after LTO (" + symName + ")");
     return;
   }
 

lld/wasm/InputFiles.h

diff --git a/lld/wasm/InputFiles.h b/lld/wasm/InputFiles.h
index 3278134..d9a8b53 100644
--- a/lld/wasm/InputFiles.h
+++ b/lld/wasm/InputFiles.h
@@ -176,7 +176,7 @@
               uint64_t offsetInArchive);
   static bool classof(const InputFile *f) { return f->kind() == BitcodeKind; }
 
-  void parse();
+  void parse(StringRef symName);
   std::unique_ptr<llvm::lto::InputFile> obj;
 
   // Set to true once LTO is complete in order prevent further bitcode objects

lld/wasm/SymbolTable.cpp

diff --git a/lld/wasm/SymbolTable.cpp b/lld/wasm/SymbolTable.cpp
index d33176a..9a381e9 100644
--- a/lld/wasm/SymbolTable.cpp
+++ b/lld/wasm/SymbolTable.cpp
@@ -23,7 +23,7 @@
 namespace lld::wasm {
 SymbolTable *symtab;
 
-void SymbolTable::addFile(InputFile *file) {
+void SymbolTable::addFile(InputFile *file, StringRef symName) {
   log("Processing: " + toString(file));
 
   // .a file
@@ -50,7 +50,7 @@
 
   // LLVM bitcode file
   if (auto *f = dyn_cast<BitcodeFile>(file)) {
-    f->parse();
+    f->parse(symName);
     bitcodeFiles.push_back(f);
     return;
   }

lld/wasm/SymbolTable.h

diff --git a/lld/wasm/SymbolTable.h b/lld/wasm/SymbolTable.h
index ef2a023..59eda1c 100644
--- a/lld/wasm/SymbolTable.h
+++ b/lld/wasm/SymbolTable.h
@@ -40,7 +40,7 @@
 
   void wrap(Symbol *sym, Symbol *real, Symbol *wrap);
 
-  void addFile(InputFile *file);
+  void addFile(InputFile *file, StringRef symName = {});
 
   void compileBitcodeFiles();