Implement getexepath for OpenBSD (#129103)

Contributes to #124911.

Author: am11

src/native/minipal/getexepath.h

@@ -15,6 +15,10 @@
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/sysctl.h>
+#elif defined(__OpenBSD__)
+#include <string.h>
+#include <unistd.h>
+#include <sys/sysctl.h>
 #elif defined(_WIN32)
 #include <windows.h>
 #elif defined(__HAIKU__)
@@ -57,6 +61,16 @@ static inline char* minipal_getexepath(void)
     }
 
     return strdup(path);
+#elif defined(__OpenBSD__)
+    const int name[] = { CTL_KERN, KERN_PROC_ARGS, getpid(), KERN_PROC_ARGV };
+    void *argv[PATH_MAX];
+    size_t len = sizeof(argv);
+    if (sysctl(name, 4, argv, &len, NULL, 0) != 0)
+    {
+        return NULL;
+    }
+
+    return realpath((char *)argv[0], NULL);
 #elif defined(__sun)
     const char* path = getexecname();
     if (path == NULL)