all: add zstd compression library

src/main.cpp

@@ -1208,11 +1208,14 @@ int upx_main(int argc, char *argv[]) {
     set_term(stderr);
 
     assert(upx_lzma_init() == 0);
-    assert(upx_ucl_init() == 0);
-    assert(upx_zlib_init() == 0);
 #if (WITH_NRV)
     assert(upx_nrv_init() == 0);
 #endif
+    assert(upx_ucl_init() == 0);
+    assert(upx_zlib_init() == 0);
+#if (WITH_ZSTD)
+    assert(upx_zstd_init() == 0);
+#endif
 
     /* get options */
     first_options(argc, argv);