Check for libzstd >= 1.1

The consensus compression code depends on a streaming compression API
that is new in libzstd-1.1.

Fixes #22413.

changes/bug22413

@@ -0,0 +1,4 @@
+  o Minor bugfixes (directory protocol):
+    - Check for libzstd >= 1.1 because older versions lack the
+      necessary streaming API.  Fixes bug 22413; bugfix on
+      0.3.1.1-alpha.

configure.ac

@@ -856,7 +856,7 @@ if test "x$enable_zstd" = "xno"; then
     have_zstd=no;
 else
     PKG_CHECK_MODULES([ZSTD],
-                      [libzstd],
+                      [libzstd >= 1.1],
                       have_zstd=yes,
                       have_zstd=no)