fix gcc 5.4.0compile errors

src/analyze.cpp

@@ -6026,7 +6026,7 @@ static TypeTableEntry *analyze_switch_expr(CodeGen *g, ImportTableEntry *import,
 
 
     int *field_use_counts = nullptr;
-    HashMap<int, AstNode *, int_hash, int_eq> err_use_nodes;
+    HashMap<int, AstNode *, int_hash, int_eq> err_use_nodes = {};
     if (expr_type->id == TypeTableEntryIdEnum) {
         field_use_counts = allocate<int>(expr_type->data.enumeration.field_count);
     } else if (expr_type->id == TypeTableEntryIdErrorUnion) {

src/codegen.cpp

@@ -2757,7 +2757,7 @@ static LLVMValueRef gen_if_var_expr(CodeGen *g, AstNode *node) {
 static LLVMValueRef gen_block(CodeGen *g, AstNode *block_node, TypeTableEntry *implicit_return_type) {
     assert(block_node->type == NodeTypeBlock);
 
-    LLVMValueRef return_value;
+    LLVMValueRef return_value = nullptr;
     for (int i = 0; i < block_node->data.block.statements.length; i += 1) {
         AstNode *statement_node = block_node->data.block.statements.at(i);
         return_value = gen_expr(g, statement_node);
@@ -3301,7 +3301,7 @@ static LLVMValueRef gen_var_decl_expr(CodeGen *g, AstNode *node) {
         }
     }
 
-    LLVMValueRef init_val;
+    LLVMValueRef init_val = nullptr;
     TypeTableEntry *init_val_type;
     return gen_var_decl_raw(g, node, &node->data.variable_declaration, false, &init_val, &init_val_type, false);
 }

src/parseh.cpp

@@ -1205,7 +1205,7 @@ static void visit_var_decl(Context *c, const VarDecl *var_decl) {
             emit_warning(c, var_decl, "ignoring variable '%s' - unable to evaluate initializer\n", buf_ptr(name));
             return;
         }
-        AstNode *init_node;
+        AstNode *init_node = nullptr;
         switch (ap_value->getKind()) {
             case APValue::Int:
                 {