[WebAssembly] Add more support for weak symbols

[sbc100]

Summary

Add weak symbol test to MC
Add symbol flags to output of llvm-readobj -t.

test/MC/WebAssembly/weak-alias.ll

+; RUN: llc -mtriple wasm32-unknown-unknown-wasm -filetype=obj %s -o - | obj2yaml | FileCheck %s
+
+; foo_alias() function is weak alias of function foo()
+; Generates two exports of the same function, one of them weak
+
+@foo_alias = weak hidden alias i32 (...), bitcast (i32 ()* @foo to i32 (...)*)
+
+define hidden i32 @foo() #0 {
+entry:
+  ret i32 0
+}
+
+; CHECK:        - Type:            EXPORT
+; CHECK-NEXT:     Exports:         
+; CHECK-NEXT:       - Name:            foo
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           0
+; CHECK-NEXT:       - Name:            foo_alias
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           0
+
+
+; CHECK:        - Type:            CUSTOM
+; CHECK-NEXT:     Name:            name
+; CHECK-NEXT:     FunctionNames:   
+; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:         Name:            foo
+; CHECK-NEXT:   - Type:            CUSTOM
+; CHECK-NEXT:     Name:            linking
+; CHECK-NEXT:     SymbolInfo:      
+; CHECK-NEXT:       - Name:            foo_alias
+; CHECK-NEXT:         Flags:           1
+; CHECK-NEXT: ...

test/MC/WebAssembly/weak.ll

+; RUN: llc -mtriple wasm32-unknown-unknown-wasm -filetype=obj %s -o - | obj2yaml | FileCheck %s
+
+; Weak external data reference
+@weak_external_data = extern_weak global i32, align 4
+
+; Weak function definition
+define weak hidden i32 @weak_function() local_unnamed_addr #0 {
+entry:
+    %0 = load i32, i32* @weak_external_data, align 4
+    ret i32 %0
+}
+
+; CHECK:        - Type:            IMPORT
+; CHECK-NEXT:     Imports:         
+; CHECK-NEXT:       - Module:          env
+; CHECK-NEXT:         Field:           weak_external_data
+; CHECK-NEXT:         Kind:            GLOBAL
+; CHECK-NEXT:         GlobalType:      I32
+; CHECK-NEXT:         GlobalMutable:   false
+
+
+; CHECK:        - Type:            CUSTOM
+; CHECK-NEXT:     Name:            name
+; CHECK-NEXT:     FunctionNames:   
+; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:         Name:            weak_function
+; CHECK-NEXT:   - Type:            CUSTOM
+; CHECK-NEXT:     Name:            linking
+; CHECK-NEXT:     SymbolInfo:      
+; CHECK-NEXT:       - Name:            weak_external_data
+; CHECK-NEXT:         Flags:           1
+; CHECK-NEXT:       - Name:            weak_function
+; CHECK-NEXT:         Flags:           1
+; CHECK-NEXT: ...

test/tools/llvm-readobj/symbols.test

 ELF-NEXT:     Other: 0
 ELF-NEXT:     Section: .rodata.str1.1 (0x5)
 ELF-NEXT:   }
 
 WASM:      Symbols [
 WASM-NEXT:   Symbol {
 WASM-NEXT:     Name: bar
 WASM-NEXT:     Type: GLOBAL_IMPORT (0x2)
+WASM-NEXT:     Flags: 0x0
 WASM-NEXT:   }
 WASM-NEXT:   Symbol {
 WASM-NEXT:     Name: baz
 WASM-NEXT:     Type: GLOBAL_IMPORT (0x2)
+WASM-NEXT:     Flags: 0x0
 WASM-NEXT:   }
 WASM-NEXT:   Symbol {
 WASM-NEXT:     Name: foo
 WASM-NEXT:     Type: FUNCTION_EXPORT (0x1)
+WASM-NEXT:     Flags: 0x0
 WASM-NEXT:   }
 WASM-NEXT:   Symbol {
 WASM-NEXT:     Name: foo
 WASM-NEXT:     Type: DEBUG_FUNCTION_NAME (0x4)
+WASM-NEXT:     Flags: 0x0
 WASM-NEXT:   }
 WASM-NEXT: ]

tools/llvm-readobj/WasmDumper.cpp

void WasmDumper::printSections() {
   }
 }
 
 void WasmDumper::printSymbol(const SymbolRef &Sym) {
   DictScope D(W, "Symbol");
   WasmSymbol Symbol = Obj->getWasmSymbol(Sym.getRawDataRefImpl());
   W.printString("Name", Symbol.Name);
   W.printEnum("Type", static_cast<unsigned>(Symbol.Type), makeArrayRef(WasmSymbolTypes));
+  W.printHex("Flags", Symbol.Flags);
 }
 
 }
 
 namespace llvm {
 
 std::error_code createWasmDumper(const object::ObjectFile *Obj,
                                  ScopedPrinter &Writer,