[WebAssembly] Read global index in init expression as LEB

[sbc100]

Summary

Also add test coverage for this case.

lib/Object/WasmObjectFile.cpp

case wasm::WASM_OPCODE_I64_CONST:
     break;
   case wasm::WASM_OPCODE_F32_CONST:
     Expr.Value.Float32 = readFloat32(Ptr);
     break;
   case wasm::WASM_OPCODE_F64_CONST:
     Expr.Value.Float64 = readFloat64(Ptr);
     break;
   case wasm::WASM_OPCODE_GET_GLOBAL:
-    Expr.Value.Global = readUint32(Ptr);
+    Expr.Value.Global = readULEB128(Ptr);
     break;
   default:
     return make_error<GenericBinaryError>("Invalid opcode in init_expr",
                                           object_error::parse_failed);
   }
 
   uint8_t EndOpcode = readOpcode(Ptr);
   if (EndOpcode != wasm::WASM_OPCODE_END) {

lib/ObjectYAML/WasmYAML.cpp

case wasm::WASM_OPCODE_I64_CONST:
     IO.mapRequired("Value", Expr.Value.Int64);
     break;
   case wasm::WASM_OPCODE_F32_CONST:
     IO.mapRequired("Value", Expr.Value.Float32);
     break;
   case wasm::WASM_OPCODE_F64_CONST:
     IO.mapRequired("Value", Expr.Value.Float64);
     break;
+  case wasm::WASM_OPCODE_GET_GLOBAL:
+    IO.mapRequired("Index", Expr.Value.Global);
+    break;
   }
 }
 
 void MappingTraits<WasmYAML::DataSegment>::mapping(
     IO &IO, WasmYAML::DataSegment &Segment) {
   IO.mapRequired("Index", Segment.Index);
   IO.mapRequired("Offset", Segment.Offset);
   IO.mapRequired("Content", Segment.Content);

test/ObjectYAML/wasm/elem_section.yaml

Sections:
   - Type:            ELEM
     Segments:
       - Offset:
           Opcode:        I32_CONST
           Value:         3
         Functions:
           - 1
       - Offset:
-          Opcode:        I32_CONST
-          Value:         5
+          Opcode:        GET_GLOBAL
+          Index:         1
         Functions:
           - 4
 ...
 # CHECK: --- !WASM
 # CHECK: FileHeader:
 # CHECK:   Version:           0x00000001
 # CHECK: Sections:
 # CHECK:   - Type:            ELEM
 # CHECK:     Segments:
 # CHECK:       - Offset:
 # CHECK:           Opcode:           I32_CONST
 # CHECK:           Value:            3
 # CHECK:         Functions: [ 1 ]
 # CHECK:       - Offset:
-# CHECK:           Opcode:           I32_CONST
-# CHECK:           Value:            5
+# CHECK:           Opcode:           GET_GLOBAL
+# CHECK:           Index:            1
 # CHECK:         Functions: [ 4 ]
 # CHECK: ...