Add back cinterop

Author: lauzadis

runtime/runtime-core/build.gradle.kts

@@ -5,6 +5,7 @@
 
 import aws.sdk.kotlin.gradle.kmp.NATIVE_ENABLED
 import aws.sdk.kotlin.gradle.util.typedProp
+import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinNativeTarget
 import org.jetbrains.kotlin.konan.target.HostManager
 import java.nio.file.Files
 import java.nio.file.Paths
@@ -33,6 +34,7 @@ kotlin {
         nativeMain {
             dependencies {
                 api(libs.crt.kotlin)
+                implementation(libs.kotlin.multiplatform.bignum)
             }
         }
 
@@ -50,17 +52,24 @@ kotlin {
             }
         }
 
-        nativeMain {
-            dependencies {
-                implementation(libs.kotlin.multiplatform.bignum)
-            }
-        }
-
         all {
             languageSettings.optIn("aws.smithy.kotlin.runtime.InternalApi")
         }
     }
 
+    if (NATIVE_ENABLED && !HostManager.hostIsMingw) {
+        targets.withType<KotlinNativeTarget> {
+            compilations["main"].cinterops {
+                val interopDir = "$projectDir/posix/src/posixInterop/cinterop"
+                create("environ") {
+                    includeDirs(interopDir)
+                    packageName("aws.smithy.platform.posix")
+                    headers(listOf("$interopDir/environ.h"))
+                }
+            }
+        }
+    }
+
     if (NATIVE_ENABLED && HostManager.hostIsMingw) {
         mingwX64 {
             val mingwHome = findMingwHome()

runtime/runtime-core/posix/src/posixInterop/cinterop/environ.h

@@ -0,0 +1,12 @@
+#ifndef ENVIRON_H
+#define ENVIRON_H
+
+// External declaration to get environment variables
+extern char **environ;
+
+// Helper function to get the environ pointer
+char** get_environ_ptr() {
+    return environ;
+}
+
+#endif