Implement os.exePath on GNU/Hurd

There is a Linux-like procfs that provides /proc/self/exe, so use the
Linux implementation of js_exepath() also on GNU/Hurd.

Author: pinotree

cutils.c

@@ -1282,7 +1282,7 @@ int js_exepath(char *buffer, size_t *size) {
 
     return 0;
 }
-#elif defined(__linux__)
+#elif defined(__linux__) || defined(__GNU__)
 int js_exepath(char *buffer, size_t *size) {
     ssize_t n;