fix: build failure using mingw

recipes/libelf/all/conandata.yml

@@ -5,3 +5,8 @@ sources:
       "https://fossies.org/linux/misc/old/libelf-0.8.13.tar.gz",
     ]
     sha256: "591a9b4ec81c1f2042a97aa60564e0cb79d041c52faa7416acb38bc95bd2c76d"
+
+patches:
+  "0.8.13":
+    - patch_file: "patches/0001-getenv-fix.diff"
+      base_path: "source_subfolder"

recipes/libelf/all/conanfile.py

@@ -82,7 +82,7 @@ def generate(self):
             tc.generate()
 
     def build(self):
-        if self.settings.os == "Windows":
+        if self.settings.os == "Windows":            
             cmake = CMake(self)
             cmake.configure(build_script_folder=os.path.join(self.source_folder, os.pardir))
             cmake.build()

recipes/libelf/all/patches/0001-getenv-fix.diff

@@ -0,0 +1,21 @@
+Subject: [PATCH] fix: Add #include <stdlib.h>
+
+---
+ version.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/version.c b/version.c
+index 7a901d3..8dc1920 100644
+--- a/version.c
++++ b/version.c
+@@ -18,6 +18,7 @@
+  */
+
+ #include <private.h>
++#include <stdlib.h>
+
+ #ifndef lint
+ static const char rcsid[] = "@(#) $Id: version.c,v 1.8 2008/05/23 08:15:35 michael Exp $";
+-- 
+2.43.0
+