https://github.com/zlib-ng/minizip-ng/pull/682

From 5aaa8bf0c348a27d9a7a0d82d4af26748278828c Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Thu, 16 Mar 2023 23:35:34 +0000
Subject: [PATCH] CMake: set newer POSIX_C_SOURCE
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Enable POSIX 2008 as it's needed for strdup(), otherwise we get:
```
/var/tmp/portage/sys-libs/minizip-ng-3.0.9/work/minizip-ng-3.0.9/mz_os.c: In function ‘mz_dir_make’:
/var/tmp/portage/sys-libs/minizip-ng-3.0.9/work/minizip-ng-3.0.9/mz_os.c:286:19: error: implicit declaration of function ‘strdup’ [-Werror=implicit-function-declaration]
  286 |     current_dir = strdup(path);
      |                   ^~~~~~
```

The man page for strdup says:
```
strdup():
	_XOPEN_SOURCE >= 500
	|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
	|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -455,7 +455,7 @@ endif()
 
 # Unix specific
 if(UNIX)
-    list(APPEND STDLIB_DEF -D_POSIX_C_SOURCE=200112L)
+    list(APPEND STDLIB_DEF -D_POSIX_C_SOURCE=200809L)
     list(APPEND MINIZIP_SRC mz_os_posix.c mz_strm_os_posix.c)
 
     if(MZ_PKCRYPT OR MZ_WZAES OR MZ_SIGNING)