Add x64 emitter tests

emit_asm_x64.c

@@ -32,3 +32,21 @@ void emit_program(FILE *file, Ast *n) {
     emit_expr(file, n);
     fprintf(file, "    ret\n");
 }
+
+void emit_expr_test(char *expr, int value) {
+    Token_Array tokens = lex_file("expr", expr, strlen(expr));
+    Parser parser = {tokens.data, tokens.data + tokens.len};
+    Ast *ast = parse_expr(&parser, 0);
+    FILE *file = fopen("out.s", "w");
+    emit_program(file, ast);
+    fclose(file);
+    int result = system("clang out.s -o out");
+    assert(result == 0);
+    result = system("./out");
+    assert(WEXITSTATUS(result) == value);
+}
+
+void emit_x64_test(void) {
+    emit_expr_test("10+5*2-10", 10+5*2-10);
+    printf("x64 tests passed\n");
+}