[WebAssembly] Check signatures of weakly defined funtions too

[ruiu]

LGTM

lld/trunk/test/wasm/Inputs/strong-symbol.ll

+target triple = "wasm32-unknown-unknown-wasm"
+
+define i64 @weakFn() #0 {
+entry:
+  ret i64 1
+}

lld/trunk/test/wasm/signature-mismatch-weak.ll

+; RUN: llc -filetype=obj %p/Inputs/weak-symbol1.ll -o %t.weak.o
+; RUN: llc -filetype=obj %p/Inputs/strong-symbol.ll -o %t.strong.o
+; RUN: llc -filetype=obj %s -o %t.o
+; RUN: not wasm-ld --check-signatures -o %t.wasm %t.o %t.strong.o %t.weak.o 2>&1 | FileCheck %s
+; RUN: wasm-ld -o %t.wasm %t.o %t.strong.o %t.weak.o
+
+target triple = "wasm32-unknown-unknown-wasm"
+
+declare i32 @weakFn() local_unnamed_addr
+
+define void @_start() local_unnamed_addr {
+entry:
+  %call = call i32 @weakFn()
+  ret void
+}
+
+; CHECK: error: function signature mismatch: weakFn
+; CHECK-NEXT: >>> defined as () -> I32 in {{.*}}signature-mismatch-weak.ll.tmp.o
+; CHECK-NEXT: >>> defined as () -> I64 in {{.*}}signature-mismatch-weak.ll.tmp.strong.o

lld/trunk/wasm/SymbolTable.cpp

Symbol *SymbolTable::addDefined(bool IsFunction, StringRef Name, uint32_t Flags,
   } else if (!S->isDefined()) {
     // Existing symbol is undefined: replace it, while check types.
     DEBUG(dbgs() << "resolving existing undefined symbol: " << Name << "\n");
     Replace = true;
     CheckTypes = true;
   } else if ((Flags & WASM_SYMBOL_BINDING_MASK) == WASM_SYMBOL_BINDING_WEAK) {
     // the new symbol is weak we can ignore it
     DEBUG(dbgs() << "existing symbol takes precedence\n");
+    CheckTypes = true;
   } else if (S->isWeak()) {
     // the existing symbol is, so we replace it
     DEBUG(dbgs() << "replacing existing weak symbol\n");
     Replace = true;
     CheckTypes = true;
   } else {
     // neither symbol is week. They conflict.
     reportDuplicate(S, F);