[WebAssembly] Fix crash when __wasm_call_ctor is GCd in programs containing static init/fini

lld/trunk/test/wasm/init-fini-gc.ll

+; RUN: llc -filetype=obj -o %t.o %s
+; RUN: wasm-ld %t.o -o %t.wasm
+; RUN: obj2yaml %t.wasm | FileCheck %s
+
+; RUN: wasm-ld %t.o -o %t.wasm
+; RUN: obj2yaml %t.wasm | FileCheck %s
+
+; RUN: wasm-ld --export=__wasm_call_ctors %t.o -o %t.export.wasm
+; RUN: obj2yaml %t.export.wasm | FileCheck %s -check-prefix=EXPORT
+
+; Test that the __wasm_call_ctor function if not referenced
+
+target triple = "wasm32-unknown-unknown"
+
+define hidden void @_start() {
+entry:
+  ret void
+}
+
+define hidden void @func1() {
+entry:
+  ret void
+}
+
+define hidden void @func2() {
+entry:
+  ret void
+}
+
+define i32 @__cxa_atexit(i32 %func, i32 %arg, i32 %dso_handle) {
+  ret i32 0
+}
+
[e-mail]_ctors = appending global [1 x { i32, void ()*, i8* }] [
+  { i32, void ()*, i8* } { i32 1, void ()* @func1, i8* null }
+]
+
[e-mail]_dtors = appending global [1 x { i32, void ()*, i8* }] [
+  { i32, void ()*, i8* } { i32 1, void ()* @func2, i8* null }
+]
+
+; CHECK-NOT: __cxa_atexit
+; CHECK-NOT: __wasm_call_ctors
+
+; EXPORT: __wasm_call_ctors
+; EXPORT: func1
+; EXPORT: func2
+; EXPORT: __cxa_atexit

lld/trunk/wasm/Writer.cpp

void Writer::createCtorFunction() {
   ArrayRef<uint8_t> Body = arrayRefFromStringRef(Saver.save(FunctionBody));
   cast<SyntheticFunction>(WasmSym::CallCtors->Function)->setBody(Body);
 }
 
 // Populate InitFunctions vector with init functions from all input objects.
 // This is then used either when creating the output linking section or to
 // synthesize the "__wasm_call_ctors" function.
 void Writer::calculateInitFunctions() {
+  if (!Config->Relocatable && !WasmSym::CallCtors->isLive())
+    return;
+
   for (ObjFile *File : Symtab->ObjectFiles) {
     const WasmLinkingData &L = File->getWasmObj()->linkingData();
     for (const WasmInitFunc &F : L.InitFunctions) {
       FunctionSymbol *Sym = File->getFunctionSymbol(F.Symbol);
       assert(Sym->isLive());
       if (*Sym->Signature != WasmSignature{{}, {}})
         error("invalid signature for init func: " + toString(*Sym));
       InitFunctions.emplace_back(WasmInitEntry{Sym, F.Priority});