Fix prototype deprecated and expression result unused,as well rewrite spec to support clang build · Pull Request !99 · src-openEuler/libreswan

# PR主要描述信息

* 此PR基于[这个oEEP](https://gitee.com/openeuler/TC/blob/master/oEEP/oEEP-0003%20LLVM%E5%B9%B3%E8%A1%8C%E5%AE%87%E5%AE%99%E8%AE%A1%E5%88%92--%E5%9F%BA%E4%BA%8ELLVM%E6%8A%80%E6%9C%AF%E6%A0%88%E6%9E%84%E5%BB%BAoE%E8%BD%AF%E4%BB%B6%E5%8C%85.md)，旨在使得该软件包可以同时支持GCC和LLVM构建。
* 不影响原来的构建行为
* 解决llvm构建时报错：
  `a function definition without a prototype is deprecated in all versions of C and is not supported in C2x [-Werror,-Wdeprecated-non-prototype]`

```c
  [  537s] error: unknown warning option '-Wno-maybe-uninitialized'; did you mean '-Wno-uninitialized'? [-Werror,-Wunknown-warning-option]
  [  537s] error: unknown warning option '-Wno-lto-type-mismatch'; did you mean '-Wno-selector-type-mismatch'? [-Werror,-Wunknown-warning-option]
  ```

`[   80s] clang: clangerror: clang: clangerror: argument unused during compilation: '-fstack-clash-protection' [-Werror,-Wunused-command-line-argument]:`

* **问题成因总结：**  第一，使用了已弃用的函数原型定义写法；第二，逗号作为语句结尾；第三，gcc的一些编译选项，clang不支持。
* **修改建议：**  第一，换成可用函数原型定义写法（已贴上游commit）；第二，逗号改为分号；第三，在spec文件中，在%if "%toolchain" \=\= "clang"判断控制条件下，去掉clang不支持的选项。

# 修复完毕

llvm构建工程：[Show home:yuncang:branches:Mega-LLVM:24.03 / libreswan - 开源软件构建与测试 (isrc.ac.cn)](https://build.tarsier-infra.isrc.ac.cn/package/show/home:yuncang:branches:Mega-LLVM:24.03/libreswan)

# 若仍有疑问，以下为问题分析与解决过程

### 问题一：使用了已弃用的函数原型定义方法`prototype is deprecated`

报错信息：`a function definition without a prototype is deprecated in all versions of C and is not supported in C2x [-Werror,-Wdeprecated-non-prototype]`

有两处，一处在上游有commit

[building: prototype maskcount() definition; clang-16 · libreswan/libreswan@e52a0af (github.com)](https://github.com/libreswan/libreswan/commit/e52a0af61990754b26a2825fb775fd5d1680112b)

另一处找不到上游对应的文件，但也可以用同样的改法

```c
size_t                          /* length required for full conversion */
ultot(n, base, dst, dstlen)
unsigned long n;
int base;
char *dst;                      /* need not be valid if dstlen is 0 */
size_t dstlen;
{
	...
}

```

改为

```c
size_t                          /* length required for full conversion */
ultot(unsigned long n, int base, char *dst, size_t dstlen)
                     /* char *dst need not be valid if dstlen is 0 */
{
	...
}
```

### 问题二：expression result unused

```c
[   97s] /home/abuild/rpmbuild/BUILD/libreswan-4.15/lib/libswan/ckaid.c:85:2: error: expression result unused [-Werror,-Wunused-value]
[   97s]    85 |         pexpect(ckaid.len == nss_ckaid_len);
[   97s]       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[   97s] ../../include/lswlog.h:489:29: note: expanded from macro 'pexpect'
[   97s]   489 | #define pexpect(ASSERTION)  PEXPECT(&global_logger, ASSERTION)
[   97s]       |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[   97s] ../../include/lswlog.h:486:3: note: expanded from macro 'PEXPECT'
[   97s]   486 |                 assertion__; /* result */                               \
[   97s]       |                 ^~~~~~~~~~~
[   97s] 1 error generated.
```

* 问题定位：

```c
ckaid_t ckaid_from_secitem(const SECItem *const nss_ckaid)
{
	size_t nss_ckaid_len = nss_ckaid->len;
	/* ckaid = { .len = min(...), } barfs with gcc 11.2.1 */
	ckaid_t ckaid = {0};
	/* should not be truncated but can be */
	ckaid.len = min(nss_ckaid_len, sizeof(ckaid.ptr/*array*/)),
	pexpect(ckaid.len == nss_ckaid_len);
	memmove(ckaid.ptr, nss_ckaid->data, ckaid.len);
	return ckaid;
}
```

发现其实是因为ckaid.len = min(nss_ckaid_len, sizeof(ckaid.ptr/*array*/)),结尾是逗号，而不是分号

该问题上游并未修复

* 修改建议：将这个逗号改为分号

### 问题三：gcc的某些编译选项，clang不支持

```c
[  537s] error: unknown warning option '-Wno-maybe-uninitialized'; did you mean '-Wno-uninitialized'? [-Werror,-Wunknown-warning-option]
[  537s] error: unknown warning option '-Wno-lto-type-mismatch'; did you mean '-Wno-selector-type-mismatch'? [-Werror,-Wunknown-warning-option]
```

经过查询，-Wno-maybe-uninitialized与-Wno-uninitialized功能不同，不能直接修改替换；

-Wno-lto-type-mismatch与-Wno-selector-type-mismatch功能不同，不能直接修改替换；

所以只能在llvm构建时将这两个选项去掉。

`[  111s] clang: error: unsupported option '--no-lto'; did you mean '-fno-lto'?`

llvm构建时，`--no-lto`改为`-fno-lto`

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